The basilica of Santa Maria degli Angeli e dei Martiri, built in the remains of the baths.

The Baths of Diocletian (Thermae Diocletiani) in Rome were the grandest of the public baths, or thermae built by successive emperors. Diocletian's Baths, dedicated in 306, were the largest and most sumptuous of the imperial baths. The baths were built between the years 298 and 306. The project was originally commissioned by Maximian upon his return to Rome in the autumn of 298 and was continued after his and Diocletian's abdication under Constantius, father of Constantine. Although many baths in and around Rome had the same elements, the Baths of Diocletian are unique by their size.

• http://en.wikipedia.org/wiki/Baths of Diocletian