I was wondering what the story is with the rope. Is there any archaeological evidence of what kinds of ropes the Egyptians used, and are you trying to duplicate that? Or are you using modern types of rope?

koven
New York

Well, we can't use what the ancient Egyptians had, because we can't get rope these days of alfalfa grass of the quality we think they would have used. So we're going for the next best thing we can get, which from the appearance of it is, I believe, a sisal hemp. It is more than adequately strong and probably on par with the strength of any rope the Egyptians had. I don't think we're exceeding the strength they would have had. We don't really know what kind of bends and hitches and knots they tied. We know they were into bindings and lashings with rope, so we'll have to go down that route.

It's a good question, because rope is the linchpin of everything we did on the NOVA programs 'This Old Pyramid' and 'Obelisk.' Pulling, lashing, building scaffolding, and rigging like they use in their boats, which they may have successfully used to raise obelisks—it all depends on rope and the quality of rope. There's a science to rope that we found out in 'This Old Pyramid.' We got a whole bunch of rope, and quarrymen who had experience in pulling heavy stones looked at it, spat, and said, 'That's no good, it's too dry.' And sure enough, when we hooked it around a three-ton block, just like that, it snapped. It has to be oiled. We're learning more and more about the power of rope.

Why don't you use the sled and A-frame idea, but then use the sled to help push the obelisk up?

(name witheld by request)

There are two major problems with sliding the obelisk down a slope on its sled. First, you don't really have control. It is not so bad on a short obelisk as with the one used in the first NOVA Obelisk program, but getting the obelisk on line as it slides is very difficult. Second, pulling the obelisk up with an A-frame requires tremendous force, because you are working against the weight of the stone all the time. Just imagine the number of people required to pull up a 400-ton stone in this manner—you are talking about thousands of laborers!

I would first cut the thing from the bottom, then use a crane and a lever.

(name witheld by request)

I'm not sure what you mean by 'cut from the bottom,' but I presume you mean an ancient crane! In a sense, we will investigate ancient lifting gear when we try to pull the butt end of the obelisk down. By combining timber members in compression and rigging in tension, we have a type of crane system off the end of the obelisk, giving us additional leverage to rotate the obelisk.

Perhaps they dug canals to the spot where they wanted to put the stone and brought it there from quarries by the river, by raft, and then dug a deep hole at the end of the small canal, and slid the obelisk off the raft and in to the deep hole while pulling on it with ropes, then filling up the canal and holding the stone in place until the earth dried—just a thought.


Austin, TX

Well, rafts are not suitable, because the amount of buoyancy available on a raft isn't sufficient—even in a big raft—to float an obelisk weighing, say, 300 tons. There has to be a boat or combination of boats. Then it's necessary to work out how they actually loaded the boats. The big problem, of course, is stability. Having no cranes, what method did they use? We hope to show that here in Egypt in the next few days.

Your Q&As lead me to two suggestions and one observation:

1. The first technique refines the pivot approach. Use rollers to move up a ramp to the height of the center of gravity, with the lower portion extending off the end. The outsides and end of the ramp should project forward on each side of the base and be stone-reinforced, leaving a clear vertical column. Attach a pivot at center of gravity, which should be over the clear column. Hang 'baskets' at each end of the obelisk with rocks for counterbalancing. Gradually shift the rocks, using ropes for control as the shifting weights do the moving. Resulting operation looks like a balance with the obelisk as the beam. (Depends on a strong pivot.)
   
   
2. Using the A-frame with pullers' ropes at the top and ropes to the obelisk at the cross beam: use two or three frames in a row to multiply the leverage, working off a ramp significantly higher and opposite the obelisk's. Pull, brace, shorten rope to obelisk; repeat.
   
   
3. Observation: the large projects such as a pyramid would have done far more than binding the nation through socialization during the period of 'draft' labor. It would have created a national language: reinforcing a 'governmental version' over dialects from remote areas; and bringing in minorities speaking other languages altogether. It also would have served as a schooling system with practical applications of writing, calculating, and engineering techniques, which would have increased commerce and the living standard. The resultant prosperity would have been a magnet to outlying peoples (such as the Israelites). The newcomers would, in turn, contribute additional knowledge, manpower, and demand, accelerating the growth.
   
   

Karl Veit
Washington, DC

The suggestion incorporates the principles of what we are trying to do in this experiment. (See 'Second Chance'.) We are attempting to use the weight of the obelisk to our advantage by pivoting it close to the center of gravity (CG). The problem with pivoting the stone exactly about its CG is that as soon as rotation begins, the CG is beyond the pivot and the obelisk wants to move on its own. This is difficult to control!

1. That's why we are placing the pivot in front of the CG so that we can rotate it to about 60 degrees before the obelisk wants to rotate on its own. At 60 percent the free rotation is easier to control. To pull the butt end of the obelisk down to get rotation, we can use two methods. The first is by using counterweights as you suggest. The second is to use men pulling horizontally on vertical ropes attached to the butt end as described by Mark Whitby in the e-mail with Andrew Kulich below.
   
   
2. The problem with A-frames is both the strength of the A-frame itself and also the number of people required to pull. Many obelisks are placed in pairs, meaning that there is no space to locate a run-off ramp beyond the obelisk for the A-frames. This would need to be positioned where the first obelisk is already standing.
   
   
3. One of the biggest lessons learned from the pulling exercise yesterday is how important organization of labor is on an operation like this. There can be little doubt that the workers, even those simply tasked with pulling on ropes, would have been well drilled and very skilled at what they were asked to do. Also, the chain of command and communication are vital in such a tricky operation. For example, you mention language. This is a major factor in our experiment. The translation between English and Arabic takes time, when decisions are often being made in split seconds. For the raising, we are considering using colored flags for certain key commands to speed up the communication.
   
   

Why not tie wood to the sides of the obelisk and divert the Nile and float it to the place it needs to go and plop it in the hole?

(name witheld by request)

This question has the same problem as the one about floating it on a raft (see above). You just wouldn't be able to tie enough wood to the obelisk to float it. It would have to be a boat.

The method for raising an obelisk would work the same way as we developed for another primitive, though modern-day monument raising in the desert, Burning Man. The technique we employ to raise our annual one-ton, 40-foot rigid monolithic structure on a flat plane, from horizontal to vertical, using human power and age-old technology, is a lever. This form of lever we call a boom.

Materials needed for proposed obelisk raising: rope, wood, people.

With obelisk lying on ground, build a four-legged tower the height of the obelisk, just in front of the base end. The tower will have to be sturdy enough that the front two legs will be able to support half the weight of the obelisk. Haul rope, strong enough to lift over half the obelisk's weight � or several ropes that sum equal strength—over the top of the tower and attach to the top end of the obelisk. The length of the rope—to be determined by how many people are spaced along it to pull half the weight of the obelisk—is fed in the opposite direction. Four guide ropes are needed: one on each side to prevent sideways swinging: one from the rear to keep from toppling forward: and one spanning from the top end of the obelisk to the top of the tower. With this last guide rope in place, remove the back two legs of the tower, allowing the tower to pivot downward as the obelisk raises.

With our boom-lever system in place, we now need only enough people to pull the weight of less than half of the obelisk (remember we're lifting the skinny end). The number of people could be further reduced by using counter-weighting and multiple booms or block-and-tackle pulleys.

Dan Miller
San Francisco, CA

This is an interesting way of doing it. The problem is that if an obelisk weighs 200 tons, you're saying you're going to have to pull over 100 tons. Now, the first thing is that the tower is as tall as the obelisk, so the angle up the side of the rope you're pulling is at 45 degrees. Forty-five degrees means you've got root 2 of the weight of the obelisk, which is 1.3. So, the 100 tons of the obelisk is now multiplied up to 132 tons, which is the pulling force.

Now, the way we calculate the pulling force for a person is that, at maximum, a person can pull his own weight. At maximum, while pulling on a rope, he inclines himself at 45 degrees, puts his weight down vertically, and pushes with his feet. If he pushes too hard, the rope pulls them back up, and the only thing countering that is his weight. This is the theory we work on. So let's say that the weight of a person is 100 weight (112 pounds), which is a slight underestimation. There are 20 of those to the ton, so to pull 130 tons, you need 20 times 130, which is 2,600 people. This is why I think this method is a little bit questionable.

Also, if you took a very tall obelisk, and the height of that obelisk is such that the tower is pulling against it is going to have to be of an equal height—that again has its own issues, in that the structure you're building is an 80-foot tower made out of bits of timber. You'd have to make it strong—yes, all is possible in this day and age, but I'm not sure that necessarily they would have gone for that. The way we're looking at it, we're going to reduce the number of people down to 150, and maybe even less than that to pull this obelisk to vertical.

To increase the mechanical advantage of pulling ropes, skip the pulleys. You can achieve greater advantage by anchoring the end of two ropes and then pull the two ropes in the middle with equal force in opposite directions perpendicular (y-direction) to the direction you want to pull (x-direction). The force exerted in the x direction is equal to two times the y-direction force divided by the sine of the angle the ropes make to the x direction. The less of an angle you have, the greater of a force you direct in the x direction. So a few people pulling on ropes tied to the middle of the main pulling ropes can exert plenty of pulling power. Think of putting a small weight in the middle of a string, then try pulling the string tight horizontally. No matter how hard you pull, you can never get the string perfectly horizontal. The heavier the weight the harder you have to pull.

P.S. I thing it was a combination of the levers to get it started, Then the above with an A-frame to increase leverage is what they used.

Andrew Kulich
Rochester, Minnesota

The method described by Andrew Kulich is exactly what we're proposing. (See 'Second Chance'.) The principle is this: We've got the obelisk with the center of gravity slightly back from the pivot point. We will need to apply a load on the base end to upset it. The first pull will be the biggest one. We'll bring it down by pulling on a frame that is fixed to the butt-end of the obelisk and that extends out beyond the end. The frame, which is very similar to frames they have on boats, will be windlass-tight to begin with.

We will have four sets of ropes come down off the end of the frame, and those will be pulled in a direction perpendicular to the lie of the obelisk. We don't want to apply a horizontal force to the obelisk, or we run the danger of pulling the obelisk forward and pulling the pivot off its bearings. So we will pull it sideways, and we will actually get a six-to-one mechanical advantage.

We will windlass them tight—we will actually lash the windlass to the pulling rope—and we'll have another pair of ropes that we'll anchor down so the butt end comes down. We'll pull those back over a block and anchor them. Then we'll release the pair of ropes, which will allow a bit of recovery in the obelisk's position. Hopefully it won't go back to the beginning, otherwise we'll have gotten nowhere. And then we'll pull again. We'll always have a long length of rope to give us a maximum mechanical advantage.

As the system develops, and the center of gravity, which is behind the roller, rotates upwards and comes to a point where it's vertically over the roller, at that point the obelisk is in balance. Any further movement will mean that the obelisk will take over and move at its own accord. At that point we'll have to be really careful. That angle is why we've set the rotation point in the place we have. What we want to do is have it as near to vertical as possible. It is quite an interesting problem; it sets up the whole geometry for the height of the ramp and everything. From that point onwards, it doesn't matter how big an obelisk you're dealing with. That's the sort of arrangement you'd like to have, because it's all similar proportions.

Might the ancient Egyptians have lost an obelisk or two in the Nile? Where would you look for them?

Alex Whitby
London, England

They obviously shipped very large things, such as obelisks and 800-ton colossi, out of Aswan. Let's say they used boats to transport them. It's conceivable that a few of these boats would not have made it. An obelisk may have been stowed incorrectly, or a boat may have been overloaded. I would have thought that it would have been very soon after their departing from Aswan that they would have capsized. It's most likely that it was very early on—once they'd got an idea of how to cope with it they would have been all right. And if they were sailing, obviously it could have been when they got caught by a strong wind.

We haven't identified a loading area near to Aswan; the bank here is pretty rocky and steep. But I think they must have found a way to drag them down to a flat site where they could pretty easily load them. I think it must be somewhere down here near Aswan.