It's all about the triangles. Math may have begun with counting, but civilization began with geometry, and this tangram-style brainteaser is inspired by the first mechanical puzzle ever to be recorded. The 3½-inch wooden square has been given 10 precise cuts, resulting in 14 pieces—most of them triangles—that must be arranged to fit back into their 4¼-inch frame. The trick is to make bigger triangles from the little ones, and there's more than one solution, though none of them are easy. Handsome enough to leave out on the coffee table for your unsuspecting guests, the puzzle is made of durable, richly stained hardwood.