pyramids and petroski

For the first time in about six years my turn has come around to teach an elective, and I couldn’t be happier to be teaching Big and Tall: History of Construction from the Pyramids to the Burj.  It’s exciting–and somewhat terrifying–to be pulling together a new course and to try to cram everything into 15 weeks, but it’s also a ton of fun.

syllabus 2015

These first couple of weeks are a mad dash through ancient building–as much about me playing archaeologist as anything else.  The point I’ll be trying to make, like virtually everything else I teach, is that designers of all stripes have aspirations they’re trying to meet, and an inevitably limited palette of resources with which to meet them.  Doesn’t matter if you’re a high-tech architect in the 21st century or a master builder in 1600 BCE.  Either way you’re being paid to perform an intricate balancing act between what Aristotle thought of as material and final causation.

So, Egypt?  Plenty of good stone, lots of labor, not so much timber.  The Pyramids or Karnak are pretty much what you get, since stone is good at holding things up, but not so good at spanning long distances.  Once you have a few hundred strengthy laborers on site you can set them going with a few tasks and not much supervision–cut this stone to size, drag it to the site from the quarry,  raise it into place, and have a mason do the final dressing.  Do that for 15 or twenty years and you get Giza.  We don’t know, of course, how exactly this got done, but the fun part about going back this far is that plenty of folks have spent time trying to figure these things out.  So, for example, how do you pull a 2.5 ton stone to the top of a growing pyramid?  Build ramps?  Rock them into place layer by layer?

Henry Petroski tossed off a particularly elegant solution.  Amateur Egyptologist James Frederick Edwards suggested in 2003 that with proper lubrication, the sloped faces of the Pyramids themselves could have supplied the (steep) ramps needed to pull stones into place:

Edwards 2004

James Frederick Edwards, “Building the Great Pyramid: Probable Construction Methods Employed at Giza.” Technology and Culture, Vol. 44, No. 2 (Apr., 2003), p. 347.

Petroski, in a subsequent column for American Scientist, added what I think is a brilliant possibility to the math.  While a gang of 50 workers could have pulled such a weight up the 52° incline, what if that gang of workers also served as a counterweight? In other words, what if the Egyptians sequenced the construction so that one gang pulled while one gang headed down the other side of the Pyramid, attached to the end of the rope pulling the next sledge?

Petroski 2004

Henry Petroski, “Engineering: Pyramids as Inclined Planes.” American Scientist, 92: 3, May-June, 2004. 221.

What I like best about this solution (aside from the fact that I get to introduce students to Petroski, a brilliant historian of engineering), is that it suggests that the resources available to the Egyptians weren’t immediately obvious.  Sure, 10,000 workers can pull a lot of stone, but they also offer a considerable amount of actual weight, which is also useful.  Especially if you don’t have very much else.  Whether the Egyptians were clever enough to realize this or not (and, remember, they hadn’t really figured out the wheel or pulleys yet), this is the kind of thinking that reveals a lot about why buildings are the way they are.  The pyramid may have been a sacred symbol, but one of the reasons the Pyramids were built, instead of the Cubes or the Dodecahedronsmay well be that the pyramidal form offered a clever way to build itself.

Fun stuff.  More to come.