Questions & Answers

Question: How do you know how much the monoliths at Stonehenge weigh? ~Jane

Answer: We know how much the monoliths weigh as we can calculate to their overall volume, including the bit that's underground, and we know what the density of sarsen, or bluestone, is. Also, some of them have actually been lifted by train while being reset not that long ago, which is also a good guide.

Question: It's one thing to drag a ten ton stone over three step middle planks. Was anyone making nice new planks 4,000 years ago? Probably a lot harder to drag a stone on rough cut timbers from ~Brad

Answer: People at this time were capable of quite fine timber work and we have evidence of this from preserved prehistoric trackways in peat bogs. So, yes, they would have been able to make smooth planks.

Question: Why was Stonehenge built? I've heard that on either the longest or shortest day of the year, the sun rises or sets just at the entrance. Why did they build it like this? ~Scott

Answer: The structure of Stonehenge is actually laid out on the line of the midsummer sun rise and the midsummer sunset, the longest and the shortest days of the year, and it seems likely that Stonehenge was built to mark these two events, which would have been enabled people to chart the changing seasons.

Question: Without the use of the wheel, the builders must have used sledges, log rollers, and many people, right?

Answer: Yes, and our experiments show that it seems more likely that some form of sledge would have been used to transport stones as log rollers are very prone to getting bogged down, particularly in softish ground.

Question: How far has the procession of the equinox moved the position of the summer solstice on the horizon since the time Stonehenge was built? ~Raymond

Answer: It has moved slightly, but not significantly enough to alter the fact that we can tell that it is this alignment that Stonehenge incorporates within its structure.

Question: On the Stonehenge raising, they used a weighted tip to tilt the main riser stone into the hole. Why not just have the stone dragged up an Earth ramp with wood rails to a pivot point of wood (timber) and just burn the timber? The loss of the support will drop the stone or is the angle too great for the raising? I can't see the stone (re: concrete) angle stone under the pivot point being used. ~Don

Answer: Burning a timber structure would, I suspect, cause a loss of control of the stone and also the heat generated would actually damage the sarsen. It's possible that any one of the stones which we now see built into the structure could have been used as that pivot stone before being erected. There are some that have a suitable cross section.

Question: Using the techniques from the show, how long did it take to build the entire structure? ~Jerry

Answer: To build the whole of Stonehenge will obviously depend on how many people you can use for the task. What we suggested was that, given a great concentration of effort, is the sarsen structures, the biggest bits of Stonehenge, could have been built within a period of three years. We suspect that probably it took longer.

Question: How do you know when it was built? ~Scott

Answer: The evidence for when Stonehenge was built comes from radio carbon dates which have been obtained largely from fragments of the antler picks used to dig the holes for the stones and the ditch.

Question: What kind of language or dialect did this ancient community speak? ~Jeff

Answer: Unfortunately, archaeology cannot give us any idea of the language that the builders of Stonehenge spoke.

Question: Why didn't they use pullleys to lift the monolith? ~Rich

Answer: Basically because it appears that the wheel had not been invented at that time and a pulley is a sort of wheel. If they did have pulleys, there is absolutely no evidence in the archaeological record.

Question: The ropes that you used, were they purchased or did you make them? ~Kenny

Answer: We purchased the ropes that we used. They were modern hemp ropes which we were obliged to use to comply with health and safety regulations. We would have liked to have made lime bark ropes to carry out the whole experiment, but this was impossible.

Question: I saw from the show that the ancients of the time had gold. Did they have any other metals? ~Robert

Answer: At the time when Stonehenge was started, no metal was used in the British Isles, but then copper, bronze, and gold were used, came into use.

Question: Where did you get stone slabs that big? ~Mike

Answer: We weren't able to get stone slabs that big. The ones we moved were replicas made of concrete. The places where both sarsens and bluestones come from are both now protected sites and it's not possible to extract stone from them.

Question: Where are the stones you have erected in this experiment now? Will they be left on this site? It appears they are a bit heavy to move. I hope to visit Stonehenge in July, hence these questions. ~David

Answer: The new trill is no longer on the site where it was erected. It rapidly became a place of New Age pilgrimage, and the farmer insisted on it being taken down the stones are currently in store.

Question: Is there an estimated population size at the time of construction that would have helped move the monoliths easier without the use of such elaborate devices that you used? ~Pat

Answer: Calculating the population which this time is very difficult because we have no clear indications of where people were living and how many settlements there were around. We felt that just using larger and larger numbers of people was not the answer, and that the builders of Stonehenge probably thought up a scheme which used less people in a safer and more controlled way.

Question: What was the closest known settlement to Stonehenge at the time of its construction, not including the area where the workers may have stayed? ~William

Answer: There are indications of settlement within a mile or so of Stonehenge, but the remains of settlements of this period are very difficult to find, in great contrast to the massive structures that that these people built.

Question: A thought occurs to me as I sit and think of the Indian burial mounds in my area: Wouldn't something like that have been useful in making the ramp for the piece on top? How old is the idea of mortice and tenon? Also, are there any writings on the stones at all? ~Patty

Answer: We know that people at this time were capable of constructing very large Earth mounds and so could quite easily have built a ramp to drag the stone up. Mortice and tenon joints, we have examples of these preserved from wet sites in this country that date back to at least a thousand years before Stonehenge, and there are no writings as such on the stones unless you count more modern graffiti, but there are carvings of daggers and axes that appear to date to the time of Stonehenge's building.

Question: I saw from the program that people were used to pull the ropes. Is it possible that beasts of burden were used for the heavy pulling? ~Sondra

Answer: It is possible that oxen were used to assist with the pulling and we would have liked to have carried out some experiments. Unfortunately, oxen, unless they have worked together before, are remarkably uncooperative beasts, and we were unable to get a team together. But this is possible.

Question: What type of marks, if any, were left on the monoliths as evidence of how they were moved? ~Keegan

Answer: There are no marks on the monoliths that provide evidence of how they were moved.

Question: In a book I read, it said that they probably put burning branches on a place they wanted to cut, then poured cold water on, cracking it. Is this what your experiment showed that they did? ~Scott

Answer: We didn't really go into the shaping of the stones, but fire is one way of breaking and shaping a stone like sarsen. It obviously carries risks, and having quarried a 40-ton block, it would be unfortunate to crack it in the wrong place. My feeling is that most of the shaping is done by pounding the surface of the stone with mauls ranging in size from footballs to small grapefruit.

Question: To move the stones, could the ancients have lashed enough logs to the stone to form a cylinder, loop ropes around the complete assembly, and pull on the upper loops to roll the stones to their site? ~Dave

Answer: This was one of the ideas that mark and I discussed and then rejected when we were thinking about how we could move the stone. It would certainly work, but could be potentially very dangerous when trying to control a 40-ton garden roller going downhill.

Question: Who owns the property on which Stonehenge is located? ~David

Answer: The land on which Stonehenge lies is owned and administered by English heritage. Effectively it's owned by the English people.

Question: Most religious practices in those days involved some sort of ritualistic or actual animal sacrifice. Is there any evidence of such at Stonehenge? ~Botkin

Answer: I don't think we can be certain that most religious practices at this time involved sacrifice and there is no direct evidence of this from Stonehenge.

Question: How did they carve out the holes in the top piece and how did they make the stone pins that fit inside? ~Mark

Answer: Both of these elements of the mortice and tenon joint could only have been made by pounding away the surface of the stone. Obviously, to make the pin, all of the stone around this would need to have been removed, leaving the pin standing proud.

Question: Could it be that the large stones were moved not on tracks, as such, but on streams or slusways for irrigation/flood control systems? ~David

Answer: Water transport would obviously be an ideal method for these large stones, but unfortunately, there are no convenient river which run between the source of the stones and Stonehenge. The route crosses high and undulating chalk downland, so this method could not have been used.

Question: Have you considered using a series of sliding fulcrums where each end of the 40-ton stone is pulled in turn, and in effect walking it balanced in the middle? I have done this with large 18th century logs for a log house with only one helper. ~Willard

Answer: Although the walking method of moving large weights can be used and was used to move some of the Easter island statues, we felt that stones of 40 tons could not be moved in this way over relatively soft ground with any degree of safety.

Question: Might the weather conditions have been different enough 4,500 years ago to use snow and ice to reduce the friction of dragging and also to build ramps? ~Ken

Answer: The weather conditions at the time that Stonehenge was built were not dissimilar from those that we find today. Ice or snow would be a great way of sliding the stones, although it would make pulling for the pullers a lot more difficult, but could not be relied upon.

Question: Were the workers forced labor, or was it perceived as a community goal with benefit for all? Who was doing the farming during the construction? ~Joan

Answer: It seems unlikely that Stonehenge was built by forced labor. We have no evidence of this in society at that time. I feel that the people probably gave their labor willingly in the construction of a monument that had significance for a great many. Obviously, there would need to be sufficient people still left to carry out the farming, although the building work could be a seasonal activity, perhaps carried out at times in the agricultural cycle when not everyone was needed to work in the fields or look after animals.

Question: If, as is estimated on the show, it took up to three weeks just to carve out the bowl for the tenon for the lintel, how long may it have taken to shape the stones themselves? How much work did they put into the shaping of the stones? After all this time, it's fairly rough-looking. ~Joe

Answer: The shaping of the stones was obviously a very laborious process. As far as how long each stone took, we obviously can't tell from their finished form how much stone had to be removed to achieve this shape. Some of them do look quite rough, whereas others are very finely finished, and we suspect that they simply chose the optimum shape as the stone came out the ground, and then shaped it as much as they possibly could.

Question: Any sense of the role women may have played in the creation of Stonehenge? ~Bob

Answer: Personally, I'm sure that the building of Stonehenge was a truly communal task in which everyone participated, whether young or old, man or woman. It's interesting to note that the depiction of the building of Stonehenge which English Heritage had on display until quite recently showed only men involved in its construction.

Question: Since there were previous wooden structures at the site, why do you think that particular spot is so special throughout time? ~Heidi

Answer: The reason why that particular spot was first chosen for the construction of a simple earthen circle and some burials is uncertain, and why that simple circle then became the focus of such an extraordinary building is equally something that archaeology can't explain. Archaeology can't get into the minds of the builders.

Question: I believe when the holes were dug, the dirt was put in a large mound in front of where two of the upright stones were to be placed. The stones were then raised to upright with a mound of Earth acting as a stop support and later as an incline to facilitate moving the lintels in place. ~Gayle

Answer: The holes that the stones were set into certainly wouldn't have provided enough soil to construct a stop or a ramp for erection of the uprights. What is obvious is that if a ramp was used, then large quantities of soil and chalk would have had to have been brought on to site and later removed. This is why I still personally feel that the use of the timber crib was more likely for raising the lintels.

Question: I am trying to figure out how the original Stonehenge could be raised by using your methods, since you required a couple hundred yards of empty space on one side of the stone and enough space to lay the stone flat in the other direction. In the pictures, these stones appear to be very close together. By the way, great job and very interesting. ~Trudi

Answer: The stones in the center of Stonehenge are set quite close together, and the requirements of space certainly seem to suggest the order in which certain elements of the building were erected. The sarsen trilithons in the center clearly had to go up before the outer sarsen circle. But Mark thinks that his methods would work, and that there was enough space to carry out in the way that he suggested.

Question: Living in rocky New England, my mother-in-law and I had to use ingenuity to move a huge underground stone in order to plant a straight row of border hemlocks on our property. I would not say we were muscular types, but my elderly neighbor showed us how to dig a small hole next to the boulder, toss in stones, dig some more, toss in a few more stones, until we actually made the bolder pop out of the ground. Might the stone age builders are used stones as leverage instead of ramps to set the Stonehenge stones upright? ~Dorothy

Answer: The difference here seems to be between moving something out of a hole in the ground and raising something up above the ground, but basically, the principle is the same: You are presumably levering your stone up onto its bed of small stones, and I think you are suggesting dragging our stone up a ramp made of small stones. Chalk was certainly easier for them to get hold of to construct a ramp in this area.

Question: Do you know if they've sunk deeper into the ground since they were first placed and erected? ~Adam

Answer: Chalk is actually quite firm bedrock and it's unlikely that they have sunk further into the ground since they were first directed. What has happened is that the surface of the chalk has lowered the solution perhaps by as much as half a meter and so less of the stone is actually set into the ground than when they were first erected.

Question: What is the purpose of a calendar that only accurately forecasts two days of the year? ~Shea

Answer: It all depends how significant these two days are, and if they are times in the year which mark significant turning points at which people can gather and celebrate, then that calendar has a lot of purpose. My feeling is still that the midwinter solstice, which is pretty close to our Christmas, was the most significant of these turning points.

Question: It was mentioned that the monoliths stand 20 or 30 feet above ground. How deep below ground level are they buried? ~Dory

Answer: The depth below ground varies quite significantly. The one that fell over and broke a couple of hundred years ago was not buried as deeply as many of the others. Anything up to about 10 feet of stone is still buried under the ones that we know, but some have never been investigated.

Question: You mentioned the use of a timber crib, since the U-shaped circle of stones in the center were after the ring. The earth ramp is limited by the area inside the outside ring, right? ~Dawn

Answer: We can't be exactly sure of the order in which the sarsen horseshoe and the outer sarsen circle were built, but common sense suggests that the inner horseshoe was built before that complete outer ring; otherwise, getting those big stones into the middle and erecting them would have been very difficult.

Question: Why did one of the largest monoliths fall over? Was it an earthquake? ~Mark

Answer: No. It was probably due to the fact that it wasn't set as deeply into the ground as many of the other stones and there is evidence that the people have been digging at the base of that stone possibly looking for treasure.

Question: Do these rock structures have any connection with the menhirs? ~Joe

Answer: There are part of the same megalithic tradition—in other words, a tradition of building using large stones of which the menhirs and alignments in Brittany are a part—and they're all constructed at roughly the same time.

Question: Considering the accuracy with which the monoliths were placed, what tools were found, not for building, but for measuring distance from the angles necessary for the use of such elaborate principles of physics to construct the trililthon? ~Brian

Answer: No measuring or surveying tools have been found from this period, but as they would presumably have been made of wood, it's not surprising that we haven't found any.

Question: I was wondering if there was any truth to the statement made by someone about the circumference of Stonehenge. I heard the circle would fit exactly inside one of the Great pyramids in Egypt, with each of the walls touching the circumference of stonehenge. Could there be some possible link between these two great mysteries? ~Alfred

Answer: I'm afraid that I don't know whether Stonehenge would fit inside one of the Great Pyramids but if it would them I'm sure that it is co-incidence. There doesn't seem to be anything else to link tie two great sites.

Question: When I visited Stonehenge in 1987 I was told that the current monument was the 6th or 7th on the site and that it had never been a place of habitation, except during the various constructions and a few religious caretakers. It is still a windy hill top without a large settlement in sight. Is this this current thinking? And, if so, what do we know of the people who built Stonehenge that they would take so much trouble in a place away from where the bulk of them lived, hunted, farmed, etc.? ~Mary

Answer: Stonehenge has a long sequence of construction and modification and I suppose that you could say that there have been several separate monuments on the same spot, starting with a simple earth circle and ending up with the elaborate stone structures that we see in ruins today. People appear never to have lived at Stonehenge itself, in the same way that people don't live in most churches. The evidence that we do have suggests that there were settlements in the vicinity at the time Stonehenge was built and used but not close by. There appears to have been a sacred area surrounding it, defined by cemeteries of burial mounds, within which people were presumably not allowed to live or farm. Just beyond this prehistoric life carried on just the same as everywhere else. The reason that Stonehenge seems so isolated today is that all the medieval villages which are the villages of today lie in the river valleys to east and west. For centuries Stonehenge has been surrounded by pasture and now arable land.

Question: I think that instead of erecting the two bigger stones and then putting the third on top, that perhaps the protrusions in the two larger stones were used to help hold the third stone on. I realize that it would take more than just these protusions but it seems to me that it might be easier to erect all three vertically at once. Perhaps incorporating your ramp to help raise all three stones. This is just a suggestion. Great show and great work. ~Mark

Answer: You are not the first one to suggest erecting the whole trilithon at one go. Personally I wouldn't like to try 90 tonnes (plus all the timber you would need to hold the whole thing together) even with the mortice and tenon joints holding the lintel roughly in place. Thanks for your comments about the show.

Question: Very little was said about the numerological (dimensional) aspects of the site. any ideas why there were the number of stones there were in the circleor why the stones were set at the specific height they were? do they align with any constellations or particular stars or is it purely a solar tool? ~Dave

Answer: We were really concentrating on the construction aspects with a bit about the site and its context thrown in. You would need a whole series of programmes to look at aspects like the geometry, astronomy etc. I personally am not a great fan of the complex astronomy idea but try looking at a book called 'Stonehenge; Science and Society' published last year which has a good article about astronomy. Basically, as far as I'm concerned, Stonehenge is a big seasonal calendar (and a wonderful place).

Question: Besides the greased rails that may have been used to move the stones, is there any evidence that the builders slid stones down hills (perhaps after a rainstorm) to take advantage of the natural terrain to ease the transport? ~Kevin

Answer: No evidence at all I'm afraid. There appears to be no trace of any route or construction but I'm sure that the builders would have used anything to make their job easier.

Question: Is it possible that the purpose of stonehenge was a sort of gateway to the heavens, what these early thought of as the transcendental realm? It seemed to me that the clustering of the grave sites around stonehenge might give a clue to this. ~Jack

Answer: Possible but the one thing that archaeology won't do is give us access to the minds of the people that built Stonehenge.

Question: 1. Why use the animal-fat-based greased "cold" - why not keep pots of it heated for continual application as needed?

Answer: I'm not sure that this would give you much of an advantage, it might make the fat too thin.

Question: Another question addressed ice/snow - but why not dig a shallow ditch to pour water in during sub-freezing yet non- snow times - stone slides on this frozen railway, but lack of snow outside it, gives traction for stone-moving team.

Answer: Possible but given unpredictable weather this could severely restrict the time that was available for stone moving.

Question: For hoisting stones, consider tripod lift structure, not just A-frame. No pulley; just run ropes over vertex. Alternately add notched post as third leg to A-frame - can rest vertex of A-frame in each notch for incremental lifts. ~Ria and Brooks

Answer: Mark and I think that a 40 tonne straight lift would have been impossible. The sort of ropes that we assume were available probably would not have been able to cope with this.

Question: I know that on the summer solstice, the sun rises directly above the heel stone, the one in the opening of the circle. If one were to draw an imaginary straight line from the center of Stonehenge and through the heel stone, is it possible that this line would intersect with the Bosporous ("Cow crossing") or Heliopolis ("Sun city") in Egypt? ~Richard

Answer: No

Question: What do you think of water being used to move the stones into position. I created a mock experiment. I discovered that a circle of wood timbers supported by the mounding of earth around them, for reinforcement and ramp, would provide the perfect arena to maneuver the stones into exact positions. The most man power needed would have been in pulling and pushing the stones up the ramp, as you demonstrated in your show, and then sliding them down into the water. Ropes secured around the stones would allow workers to move into place with much less man power than expected! I think this theory has merit. This method could be accomplished without the wheel pulley's or hundreds of men. Perhaps they even made a ravine filled with water to move the large stones using beasts of burden over (below) ground to their destination? This theory has merit. I'm interested in your thoughts. ~Brian

Answer: I'm not sure exactly what you are suggesting and can't see the advantage of having the stones in water (they would sink - or have I missed the point). There is a problem too as Stonehenge lies on chalk which is probably the most porous sort of bedrock that you can find. There is no evidence of a water channel (canal) to transport the stones in and there would be a problem here too as the route that the stones would have to take is over very undulating terrain.

Question: If they used one A-Frame could they have linked two or three of them, and reduced the effort more? ~Doug

Answer: Possible, but I suppose there comes a time when the construction of more and more A frames is more trouble than rounding up a few more volunteers. It's a good thought though.

Question: Is it possible that Stonehenge was created as a place of healing for those with nasty contagious diseases? That might explain who paid for the work (the wealthy who had taken ill). It might also explain the burial mounds (quarantine areas) and way the burial mounds were ranked with the wealthiest men being closest to Stonehenge. The fact that at least some of the gold artefacts were not stolen from the barrows might indicate that people were afraid to go near these places Also doesn't it seem possible that the fellow that used the ramp to cap the trilithon got it right. If you were going to excavate enough earth to place a 40-ton stone would you not want to utilize the product of your labor to make a ramp? This would also enable these people to raise and cap the trilathon in one day. Maybe during an elaborate ceremony to celebrate the work. ~Brad

Answer: Lots of things are possible with Stonehenge but I haven't heard the idea of the wealthy and infirm funding it before. I'm not sure about your ideas concerning quarantine. Regarding the ramp, the volume of chalk that you would get from the stonehole is comparatively tiny compared to that which would be needed to construct a ramp (maximum of eight cubic meters compared with at least 100 cubic meters). How would this enable the people to raise and cap the trilithon in one day? I am quite sure that however it was done there must have been a celebration when they finally completed the building work.

Question: I noticed several questions about using pulleys. I, too, thought of this idea, and considering how simple it is to make a wheel, I am wondering why you think the wheel hadn't been invented. Also, considering that wood would not last these thousands of years, why would you expect to find any archaeological evidence of pulleys? I think you are underestimating the intelligence of these ancient engineers. Also, do you have any _real_ engineers working with you? I doubt you, as archaeologists, have nearly the mechanical know-how or ingenuity of even the least intelligent ancient engineer. ~Daniel

Answer: As archaeologists we have to take the absence of evidence seriously. There have been enough excavations of waterlogged sites with artefacts of all types surviving (but no wheels) to lead us to believe that the people that built Stonehenge were not using the wheel. Of course we don't underestimate the intelligence of the ancient engineers. You seem to have overlooked the fact that Mark Whitby, who played a central role in the experiment that was part of the NOVA program, is a "real" engineer. I am sorry that you have such a low opinion of archaeologists; maybe we don't have the accumulated skills of an ancient engineer (even one of the least intelligent ones) but we do have a genuine love of the past and a healthy respect for its inhabitants.

Question: You've probably answered the concepts of "counterweights" a million times, or even the compulsion for it. With buckets, ropes, logs, ramps, sand and/or rocks - progressively increased sizes of rocks - could these wonders have been built by just a few folks? Is there a technically disqualifying aspect of this concept or simply a, "why SHOULD they use counterweights"? ~Lee

Answer: Theoretically it would be possible to move large weights by using a small weight to help move a larger one, etcetera, but I think the idea of Stonehenge being the work of a small group of people is unlikely. You certainly couldn't move the big stones in this way.

Question: I was wondering if it would be possible if they could have built a hill over the entire area. Then simply dig a hole or possibly used forms before the dirt was hauled in. In this manner the large stones could be set in place in much the same way as shown on May 5. I would have to see a Geothermal map of this area to be able to tell if there were any large holes dug that would suggest this. ~Randy

Answer: Theoretically possible, but unlikely. The volume of chalk and soil required would be huge and there are no signs of any quarries in the vicinity of Stonehenge which could have provided this material,

Question: Could there be any link between Stonehenge and other large stone works elsewhere on earth, such as the pyramids? As there is no reliable written history, could the "giants from Africa" be Egyptians, or another race, and isn't it funny that they all came from relatively the same time period?.....the workmanship is a little different, but still, the tactics used to move large pieces of stone seem to be the same, at least in modern re-creations............. ~Jay

Answer: Although it is tempting to see similarities between Stonehenge and other large stone structures, the only ones which have a real link are the great alignments and other megalithic structures in Brittany. The idea of the architecture of Stonehenge coming from the Mediterranean area (or even from further afield) effectively died when radiocarbon dates became available and showed that Stonehenge was older than all the civilisations that were supposed to have influenced its design and construction.

Question: You mentioned that Stonehenge was erected 4500 years ago. How many 1000s of years ago did human first habitate in this area (U.K.)? I always thought the Mediterannean (Egyptian) area was one of the first locations for human inhabitants. Am I correct when I say that was about 2000 BC? ~Scott

Answer: There has been human (or initially hominid) occupation of what was to become the British Isles since about 500,000 BP. After this various ice ages meant that there were no people around for long periods. Further south in Europe and beyond they didn't have to contend with ice so there has been habitation for even longer. There isn't the time to go into this in detail but, suffice it to say that people had been around in the areas that I have mentioned for a very long time by 2000BC.

Question: I visited Stonehenge when I was eight. I do not remember the dimensions. But, is it possible that all three pieces of a trilithon could be raised together? Perhaps tied together and lashed to a wooden frame, then raised? I believe this would be labour intensive, but more simplistic in engineering it. Has anyone tried? ~Bill

Answer: No one has tried to raise the three components of a trilithon together. The whole thing would weigh about 90 tons, not counting the timbers that you would need to hold it together for the lift. It certainly couldn't be done for the Great Trilithon as we know that the two uprights are of unequal length which would make this method impossible.

Question: I have heard a brief mention of a way that someone could lift a mega ton stone. By finding the Zero gravity spot on these stones single individuals could lift massive tones with ease. Have you heard of such an explanation? Is there any proof that this could be possible? ~Jim

Answer: I'm not sure what the zero gravity spot is but it seems to be against all the laws of physics.

Question: In the Stonehenge project, what if the hole that was dug for the vertical stones was "c" shaped so that the stone would slide in, then use its own momentum to stand itself erect? Is this possible? Thanks for your input. ~John

Answer: I don't think that the stone would stand itself erect in the base of a "c" shaped hole. You would have to balance it there before packing it firmly in place and I think that it would be potentially much more unstable than if it was in a hole with one vertical and one ramped side.

Question: The show was very interesting. However, the people in the show forgot about the one resource that the people back then had. That was time and lots of it. The construction of Stonehenge may have taken many many years, not the short period of time that the show seemed to be portraying. The stone age people also undoubtably used many many more people than the show did. They may have also used captured enemies to do the work also. The cap piece could have been "walked" up the ramp by pulling on one set of ropes at a time, effectivly doubling the manpower. Did the stone age people know about the block and tackle or even an early form of it? Overall, though, a very educational and wonderful show. Please keep up the great work. ~Clifford

Answer: We are quite aware that people had a lot of time and we did not intend to imply that Stonehenge was built in a short period of time. What we showed was that it could have been built in a shorter time than many people estimate. I disagree that they undoubtedly used many more people than we did. As numbers grow then the ability to co-ordinate effort lessens.. Prof Atkinson suggested that over 1000 people were needed for some of the tasks, but such an army of labourers would have been well nigh impossible to manage. I disagree about "captured enemies" - there is no evidence for slavery in the British Neolithic/Bronze Age. We have no evidence for block and tackle (the wheel was not used until much later). Sorry to disagree with so many of your points. Thanks for your comments about the show.

Question: Would it not make sense to only roughly cut the stones at the location in a cylindrical form and roll them to the final assembly point, where the final square cutting would be performed? Do the dimensions of the uprights + the dimensions of the topping stones add to a cylindrical shape? The tracks seem to be way too much capital and human investment for the task at hand. Does the quarry have evidence to show the stones were cut square at the site? Another method would be to build wooden craddles shaped like wheels for either end (actually best if placed at 1/3 and 2/3's of the length) of the stone, using the stone as the connecting axle. Clearly from the shape of the final building and the burial mounds the concept of the circle, and hence the wheel, was probably well understood. Enjoyed the program but agreed with the analysis that the solutions were over engineered. ~Jon

Answer: The sarsen stones at the place where they originate are found largely as flat slabs (sarsen is a sedimentary rock). It is therefore unlikely that any of cylindrical form would be found which could be rolled as you suggest. Regarding the quarry - the stones are not cut out of solid rock, they exist as detached slabs of rock embedded in redeposited chalk. Why do the tracks seem too much capital and labour investment for the task? You would only need to make a short length of track which could be taken up and relaid in front of the sledge and stone. If it makes the task easier then it would be well worth it (there are earlier sophisticated and well constructed Neolithic wooden trackways in peat bogs in nearby Somerset). Despite the circular henges and barrows there is no evidence of the wheel at this time. Glad you enjoyed the show.

Question: Could you have tipped the large stone to vertical by men pushing the top with timbers and driving wedges or filling with stones behind? Also, were the pits dug that deep? Wouldn't a considerable amount of silt layers have accumulated over the thousands of years? ~Bruce

Answer: I think it would be difficult to generate enough force to tip the stone by pushing with timbers as you suggest. Wedges would help but filling in with stones behind can cause problems if they trickle round the sides and front and hinder moving the stone to upright. The pits were dug that deep, the stones put in and then the remainder of the hole packed tight with stones and chalk. No room for silt to accumulate.

Question: During the NOVA program, raising Stonehenge, the question of the methods used to erect the stones was bandied about, in particular how the lintels were raised. Simply put has any stratagraphic analysis of the soils around Stonehenge been done with an eye to spoils piles removed from putative dirt ramps? Could these piles be detected to this day by virtue of the disturbed strata and presumably undisturbed soils in the area of the monument? ~Don

Answer: The soils over the chalk are very thin in the vicinity of Stonehenge and there is no sign of the spoil from an earthen ramp. There is also the question of where the chalk etc would have come from in the first place. You may gather that I am not a fan of the ramp idea and prefer the timber crib method.

Question: I had thought that the stones in Stonehenge were of a sort that came from Wales? Sorry to make your Herculean effort sound trivial but perhaps boats were used to bring to a spot even further than yours? Also how does one use bronze tools to cut rock? Thank You for you foray in History. ~JTB

Answer: It's the smaller stones, the so called "bluestones" that come from further afield, from the Preseli mountains in Wales to be precise. It is suggested that they came part of the way by water. This can't be the way that the larger Sarsens were transported, as there aren't any convenient rivers that run from the place where they are found to Stonehenge. You can't use bronze tools to cut rock, except very soft ones like chalk. You certainly can't cut sarsen with bronze—even iron makes little impression.

Question: I think the idea of the A-Frame lever was very good. Why not use another mechanical advantage for transporting the stones, namely a pulley? Rope is affixed to a post in the ground, run around a post attached to the stone, then pulled upon by the pullers. 2X advantage! ~Dave

Answer: We didn't use a pulley because there is no evidence for pulleys, or for any other type of wheel, from this period in prehistory.

Question: What was the average life span of the stonehenge builders? ~Scott

Answer: We have no firm evidence about the average life span of people at this time. Many people have the idea that life was "nasty, brutish and short" but human bone specialists may have been routinely underestimating the age of people at death and there is no reason why you couldn't survive at least into your 50's if not beyond. It might seem simpler but the forces required to raise this would be huge. We know how much the monoliths weigh as we can calculate their overall volume (including the pit that is underground) and we know the density of sarsen (or bluestone). Also, some of them have actually been lifted by crane while being re-set which is also a good guide.

How can I avoid eating food with ‘forever’ chemicals?

Across the country, states are banning forever chemicals from consumer products, and some companies are promising to phase out use of the compounds.

But what are we supposed to do in the meantime?

“Forever chemicals,” or PFAS, which stands for per- and polyfluoroalkyl substances, are known for their persistent ability to remain in nature — and the body — for years. Certain PFAS have been associated with serious health effects, including infertility, high blood pressure and some cancers, according to the Food and Drug Administration.

Cindy Luppi, the national field director for Clean Water Action, said “it’s very hard” for people to avoid products with PFAS.

“For the average consumer, there’s no way to avoid it,” said Graham Peaslee, a physics professor at the University of Notre Dame. “But, you can do some smart things.”

We spoke to PFAS experts about the steps you can take to minimize exposure from the foods you eat. Here’s their advice.

Grease-resistant fast-food packaging that keeps oil and meat juices from spilling on your clothes often also contain oil-resistant PFAS. This includes the paper wrappers, boxes and other containers used to serve burgers, fries and salads from fast-food chains.

Your risk of exposure to PFAS depends on the “contact time” — the time the food has spent inside of that plastic bag or paper wrapper, said Jamie DeWitt, professor of pharmacology and toxicology at East Carolina University.

Last year, Consumer Reports tested more than 100 food packages and reported higher levels of PFAS in wraps, trays and bags from Burger King, McDonald’s, Chick-fil-A and Cava, among others.

The properties that make PFAS such useful compounds for oil-resistant fast-food wrappers (and rain coats) are the same reason these chemicals can then stay in the body.

“These chemicals are unique because of their ability to cause harm at such low levels,” said David Andrews, senior scientist at the Environmental Working Group, adding that the chemicals can prove to be a health concern at “parts per trillion” in drinking water. “They actually stick to our blood, and they tend to accumulate in our bodies.”

In recent years, a number of major companies, including McDonald’s and Burger King, have stated they’re planning to reduce or phase out the use of packaging with forever chemicals.

Consumers can be frustrated because there’s no simple way to test products for PFAS, and the chemicals aren’t included on ingredient lists. Switching from packaged to fresh foods that don’t spend as much time on the shelf can reduce your risk of exposure.

“In general, food packaging is a source of contamination,” said Melanie Benesh, vice president of government affairs at the Environmental Working Group. “The fewer packaged foods that you are eating, the less likely you may be to be exposed.”

Some packaged foods are potentially exposed to PFAS in materials longer than others.

Some experts discourage frequent consumption of prepackaged microwave popcorn because the kernels are often sitting in that package of oil and other flavoring for an extended period of time.

Keith Vorst, an associate professor and the director of the Polymer and Food Protection Consortium at Iowa State University, said that when we heat up food in paper linings or plastic containers there’s a risk that some PFAS potentially coating the packaging can turn into a vapor and contaminate what we eat.

But, “we don’t know” what the risk of exposure is, Vorst said. “That is one area that we need to do some work in.”

It’s also not clear how much of our exposure to PFAS comes directly from the food supply. The FDA tested for 30 different types of PFAS in samples of 718 foods. It found 701 of the samples to be free of PFAS. Experts say the study was too limited in scope to draw broad conclusions because there are thousands of PFAS in use.

The testing of the food supply needs to be comprehensive, Andrews said.

Nonstick pots and pans are often coated in a material with PFAS. Peaslee said he has switched to ceramic cookware, and his eggs “are no worse than they used to be.”

“Be a little wary of things that are marketed as nonstick or stain resistant or water resistant,” Benesh said.

Cooking with stainless steel or cast-iron pans isn’t just about protecting yourself from these forever chemicals, DeWitt said. Your potential exposure from a nonstick pan may not be significant, but that doesn’t consider what it took to create the pan.

“The production of that pan is going to negatively impact other people who are bearing the brunt of the pollution that is produced when that nonstick coating is manufactured and applied,” DeWitt said.

Experts recommend storing leftovers and other food in glass containers, not plastic, in the fridge.

“Move away from plastics wherever possible,” Luppi said. “That’ll be one relatively easy and cost-effective thing to do.”

Check the results of water testing where you live and consider adding a water filtration system at home. Carbon filters on faucets or in water pitchers can reduce the levels of PFAS, if the filters are replaced regularly, Andrews said. Reverse osmosis systems installed under sink faucets “can typically eliminate the PFAS contamination.”

Andrews said these systems “typically cost a couple hundred dollars but can be more effective at removing PFAS.”

Your water supplier should provide water testing results. In March, the Environmental Protection Agency proposed drinking-water standards that will require water utilities to reduce levels of PFAS contamination.

The low-density plastic used for bottled water is not considered a potential source of PFAS contamination, Peaslee said. Unless a manufacturer makes a specific safety claim about PFAS, there’s no way for a consumer to know if the bottled water itself has been tested. “Bottled water is a lot safer than drinking a contaminated well with PFAS in it,” Peaslee said.

PFAS have been widely detected in freshwater fish. Last year, the FDA conducted a “targeted seafood survey” and detected PFAS in 74 percent of the seafood tested, including in clams, cod, crab, pollock, salmon, shrimp, tilapia and tuna.

“The data on PFAS in seafood is still very limited,” the FDA wrote in a report on PFAS in foods. “However, our testing indicates that seafood may be at higher risk for environmental PFAS contamination compared with other types of foods.”

Locally caught fish is more likely to have higher PFAS levels than farm-raised fish, experts say. Check statewide advisories before eating a recreationally caught fish. The FDA says people should continue to eat a “variety of healthy foods, including seafood.” The agency found the levels of PFAS detected in most of the seafood products tested did not appear to pose a “human health concern.”

“Be cognizant of fish advisories,” DeWitt said. “Consume fish because it’s healthy for you. But, don’t eat fish for every meal every day.”

Do you have a question about healthy eating? Email EatingLab@washpost.com and we may answer your question in a future column.