Castel Sant'Angelo National Museum
The Castel Sant'Angelo is actually a tomb, Hadrian's Mausoleum. The Roman Emperor built it for himself and his family; their ashes were placed there in 138 AD. Other emperors are also buried there, but the tomb became a fortress in 401 AD; in 410 it was raided and the ashes were scattered. It is likely that Hadrian himself ended up in St. Peter's where a lot of the finest ornamentation of the mausoleum and other Roman buildings were taken.
It was named Castel Sant'Angelo after 590 AD when the Archangel Michael is said to have appeared on top of the building, signifying the end of the plague. From the 14th century, the popes turned the place into a residential castle, connecting it with St. Peter's by a fortified corridor. Since 1925, it has been a museum. The complex maze of rooms and corridors now house beautiful furnishings, paintings, sculptures, archaeological finds and historic weapons.
The most beautiful way to approach the Castel Sant'Angelo is to walk across the bridge Ponte Sant'Angelo with its white marble sculpture angels by Bernini. The bridge is easily reached on foot or by taxi from the center of Rome. You can also start at St. Peter's and, walking with your back to the Basilica, you'll find the Castel Sant'Angelo beside the Tiber River.