Why were pies in the 1600s baked in such improbable shapes? Over at HiLobrow, Tom Nealon investigates, and Deb Chachra drops some science on the question.
Chachra, an engineering professor, offers this hypothesis:
Why are the shapes of the pies so fabulously baroque compared to today's plain round or square pies? One reason might be to help provide structural integrity to a high-walled pie that wasn't baked in a supporting tin. Thin walls tend to buckle or fall over when they're flat; adding an angle or a curve makes them much more stable. (You can see this by trying to balance a piece of paper on its edge, then folding it in half and trying it again.) Especially in the larger pies, having scalloped or sharply curved edges would make the pie walls more stable without having to use a thicker crust. The same principle can be seen in crinkle crankle walls, serpentine walls that are usually only one brick wide — the alternating curves means that the wall can be made very thin, while still not falling over (and thus use fewer bricks). Of course, using different patterns of curves and angles for each type of pie may also help differentiate the contents, and would also provide different ratios of crust to filling for different kinds of pies.
Nealon's has some really funny history in it, so it's worth reading the whole piece.