It's Egyptian in style. Made from slave-cut limestone and imbued with otherworldly powers that normal humans can't comprehend. Alien races are often attributed with the engineering principals, but it was slave labor that made them, ultimately. Even in the age of the Pharoahs it was The Man keeping us down.
Actually, it refers to the triangular shape of the limb's profile and not the cross section of the limb. In cross section it would be rectangular (if made from a board opposite sides would be parallel. But if made from a stave, the back of the bow would be slightly arched from the outside circumferance of the tree). Pyramid bows taper in width from the widest point just below and above the handle area down to the tips. Because you are narrowing the limbs consistently from grip to tip the bow limb often remains a consistent thickness from widest point to the tips. Clear as mud? Good. My work here is complete.
Pyramid bows are pretty efficient shooters, fairly easy to make from a board when you don't have a lot of experience with tillering, and work great with lighter target arrows. The broad part of the limb just seems to beg the maker to indulge in some geometric artistic expression, for some reason. Something about that otherworldly powers these bows have.
