Its construction was commissioned by Hadrian in the 10th-12th century as a tomb for himself and his successors. Created by the architect Demetriano around 123, from 1925 is the Rome headquarters of the National Museum of Castel Sant'Angelo, home to memorabilia and works of art.
The building has a square base of 89 meters, above which stands a second cylindrical building, above still a small circular temple surrounded by columns and the statue of the Archangel Michael. The stratified structure is due to the three different historical periods that Castel Sant'Angelo had to face.
Over the years the mausoleum became in fact a fortified citadel with towers, battlements and loopholes used as defense, later became the residence of popes and was incorporated into the Vatican walls. The wars destroyed all the statues that adorned the mausoleum, transforming it forever into a castle. St.Angel Castel still underwent several changes: in 1534-49 with Paul III who built the large loggia with five arches towards the Castels'Prati, in 1559-65 with Pius IV who built a large pentagonal wall around the old wall of and in 1623-44 with Urban VIII which had the front fortifications destroyed and a large front wall was built. In the nineteenth and in the rebirth the castle became a political prison and fell into degradation. In the nineteenth and twentieth centuries it was restored again but lost many original architectural forms and traces.