You might think that with the Egyptian pyramids being famous for thousands of years (they’re the only one of the Seven Wonders of the Ancient World still standing) there wouldn’t be much new to say about them. But you’d be wrong. The Egyptians wrote down virtually nothing about their architectural methods; they may have worked with some kind of 3-D models – the Bronze Age version of Computer-Aided Design – rather than anything like blueprints. So we haven’t really known much about how the pyramids were built. In particular, it’s been a real puzzle how they moved building blocks to near the top of the pyramid in the later stages of construction. If blocks were moved along a straight ramp up the side of the pyramid, the ramp in the last stages would have had to be a mile long, and contained as much material as the pyramid itself. It also wouldn’t have fit on the Giza plateau. Recently, Jean-Pierre Houdin, a French architect, may have figured out how the problem was solved in the case of the largest pyramid, the Great Pyramid built for King Khufu (Cheops). According to Houdin, the builders used an external ramp for the early stages of construction. But they also built a vaulted internal ramp, spiraling around insidethe pyramid, and moved blocks up it for the later stages. (And the builders economized by dismantling the external ramp and using it for construction material.) Houdin revealed his theory in 2005. Both before and since then he has put a huge amount of work into understanding how the Great Pyramid was built. For example, he may also have come up with an explanation for the 150 foot-long, narrow, slanting Grand Gallery in the pyramid: it looks like it was used to run counterweights on a trolley that helped to bring up some of the heaviest stones, the granite blocks used to reinforce the King’s Chamber.