It was Used as shelter for popes and as jail. To make it safer in 1277 it was joined to the Vatican by the famous "Passetto". This long fortified passageway allowed the pope to walk safely from the Vatican to Castel Sant'Angelo. Today it is a Museum (National Museum in Castel Sant'Angelo). There are collections of weapons and documents about the history of the castle. All rooms can be visited, from the jail to the pope's apartments and all the numerous fully adorned rooms. You can see: Apollo's room with frescoes by P. del Vaga's school; Leo X's chapel with Renaissance sculptures; Clemente VII's rooms with works by G. Romano, T. Cats, L. Signorelli and others; Paul III's loggia by R. da Montelupo; Giulio II's loggia by Bramante; Paul III's apartment with the Paoline room decorated by P. del Vaga, D. Beccafumi and others; Adrianeo's room and the Festoons' room with ST. Jerome painted by L. Lotto.