Subsequently the fortress was ransacked by the Lansquenets, then restored by Paul III and bombed by the Spaniards. A center of the military power for the pontiffs, it lost its importance when in 1557, following a flood, the riverbed of the Tiber was diverted away from the fortress.
Castello di Ostia, Ostia (RM), Lazio, Italy
The castle is divided into a residential area and a military zone. In one of the circular towers, there is a peculiar helical staircase not supported by anything: each of the steps is integrated for one third inside the walls of the tower and discharges all its weight on the following step.