Basilica of Santa Sabina

Built around 425 AD on the Aventine Hill, this is the most architecturally pure surviving early Christian basilica in Rome — almost entirely unchanged from its original form. Serene white marble columns line a long luminous nave, with translucent windows of selenite (not glass) filtering milky light. The ceremonial cypress doors at the main entrance, carved around 432 AD, bear what is probably the earliest known depiction of the Crucifixion — easily missed because they're often closed (enter via the side door). The mother church of the Dominican Order; Saint Dominic himself lived in the adjoining monastery, and his orange tree (planted 1220) reportedly still grows in the cloister.