Of the 900 baths in Rome in the 4C, those of Diocletian were the largest and finest; covering 13ha, they could accommodate 3 000 people, and were built by 40 000 Christians condemned to hard labour on account of their faith. It was this last fact which in 1561 prompted Pope Pius IV to build Santa Maria degli Angeli on top of a section of the baths. Also to be found here is the Museo Nazionale Romano (planetarium).