The Praetorium, the Roman Governor's Palace of Upper Germania, Cologne

The Praetorium in Cologne sits beneath the modern city as a sprawling stone skeleton of the Roman governor's palace. Its defining feature is a series of thick, vaulted foundation walls that once supported the seat of power for Upper Germania. During the third century, Roman officials governed the province from this site, overlooking the Rhine. In one of the halls, archaeologists recovered a marble head of the emperor, discarded face down in the dirt when the city fell to Frankish invaders.