Photo: Ulrich Mayring · CC BY-SA 3.0 · via Wikimedia Commons
Mud Flood · Rome, Italy
Basilica of San Clemente
The open question
Why fill an entire building with dirt and build on top instead of clearing it?
On the record
Three layers: a church built just before 1100, on top of a 4th-century church, on top of a Roman house and a 2nd-century mithraeum. In the 4th century the lower level was filled with dirt and rubble.

