Civita di Bagnoregio Geography

The geology here is unusually easy to read because it is doing something visible. A cap of hard volcanic tufa sits on a thick bed of soft marine clay. Rain works into the clay, the clay slumps, and the tufa above it loses support and breaks away in blocks.

The result is the calanchi — steep, bare, deeply gullied badlands running down either side of the ridge. They are spectacular and they are the mechanism of the town’s destruction.

Civita was once joined to Bagnoregio by a saddle of land carrying a road. That saddle has gone. Two rivers, the Torbido and the Chiaro, cut the valleys on either side, and the two settlements now face each other across an open gap.

The wider area is the same volcanic country as the rest of the Tuscia, with Lake Bolsena — a crater lake, the largest in Europe — about fifteen kilometres west.