Sandra Miesal, debunker of Di Vinci Codes and writer, has a useful and focused article ("Beyond Basilicas") on the early churches that were not build in the rectangular basilica form. She talks about the octagonal San Vitale in my favorite church touring place, Ravenna. I am grateful to Shawn Tribe for the link.
When the reformers renovated the mass after Vatican II, they had a number of assumptions or presumptions. One was that the priest faced the people in the early church. They appear to have been quite innocent of the architectural record. As Miesal says, "Regardless of design, the main altar normally stood in the east of the building, not the center." The liturgical reformers were either ignorant of or ignored this fundamental evidence enfleshed in stone.