I'm surprised there's no mention of Byzantine Prosphora as a comparison. It's an ancient breadmaking tradition, Roman in origin, and still in widespread use tod

I'm surprised there's no mention of Byzantine Prosphora as a comparison. It's an ancient breadmaking tradition, Roman in origin, and still in widespread use today in Eastern Orthodox churches. Although it doesn't have the eight slices of Panis Quadratus, it does have the distinctive ridge in the middle, formed by taking two circular discs of dough and pressing them together with a stamp. This seems to me at least as likely of a theory for the ridge in the middle, as wrapping a bit of twine around it solely for the purpose of making the indentation.