Castel Sant' Angelo, Rome

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Castel Sant'Angelo, is a towering cylindrical fort initially built by the Roman Emperor Hadrian as a mausoleum for himself and his family. Roman emperors continued to be placed here until 217. After this it was adapted for use as a fortress. From the 14th century, the popes converted it into a castle. It was decommissioned in 1901 and is now a museum.
The Columns also date from Roman times.