Castel Sant' Angelo
Castel Sant' Angelo (kästĕl´ säntän´jālō), Hadrian's Mausoleum, or Hadrian's Mole, massive round construction on the right bank of the Tiber in Rome. Originally built (AD 135–39) by Emperor Hadrian as a mausoleum for himself and his successors, it was later decorated and fortified as a place of refuge for the popes and was connected to the Vatican by a secret passage. It was used as a fortress and prison until 1870 and is now a museum.
"Castel Sant' Angelo." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (March 19, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/castel-sant-angelo
"Castel Sant' Angelo." The Columbia Encyclopedia, 6th ed.. . Retrieved March 19, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/castel-sant-angelo