The Basilica of Maxentius is the moment Rome carries its bath engineering into a civic 'assembly hall' typology — a typology that, a few centuries later, becomes the skeleton of the Christian church. Classical Roman basilicas (law-court and commercial halls) were generally long timber-roofed spaces lined with columns. Maxentius instead applies the groin vault of the baths to a civic hall at great scale.

The building is composed of a tall central nave roofed by three giant groin (cross) vaults, with lower barrel-vaulted side aisles to either side. Load is transferred not to columns but to massive piers and to the vaults of the side aisles; the side vaults act as buttresses meeting the outward thrust of the central nave. This is the early, heavy-massed version of the idea — balancing lateral thrust through the roofing system — that the Gothic cathedral will refine centuries later. Clerestory windows in the high walls of the central nave admit light from above.

The plan — tall central nave, lower aisles, an apse at one end, light from above — is almost exactly the scheme of the later basilican church. When Christianity, as the religion of empire, needed a large congregational space, it took as its model not the small, inward-turned cella of the pagan temple but this public hall. The Basilica of Maxentius thus carries two histories at once: the peak of Roman concrete-and-vault engineering, and the unborn plan of Western church architecture.