Santa Maria degli Angeli e dei Martiri
, usually known only as Santa Maria degli Angeli, is a titular basilica church in Rome, built inside the frigidarium of the Baths of Diocletian in the 16th century, dedicated to the Blessed Virgin Mary, to the angels and to the Christian slaves who died building the Baths of Diocletian. It is on the Piazza della Repubblica, and near the Termini train station.
For reference, a plan of the church is available here
The church was built in the remains of the Baths of Diocletian by orders of Pope Pius IV (1559-1565), after a Sicilian priest, Fr. Antonio Del Duca, had a vision of angels in the ruins in 1541. Michelangelo designed it and started the work in 1563, and after his death in 1564 (incidentally the same year that Fr. Del Duca died) his design was completed by Jacopo Del Duca, nephew of Fr. Antonio and pupil of Michelangelo. Although the interior has changed considerably and the floor has been raised a few feet, this is one of the places where you can best appreciate the size and splendor of the imperial baths.
The church was granted to the Carthusians, who moved from their former monastery at Santa Croce in Gerusalemme. They had a monastery built adajcent to it, possibly to a design by Michelangelo. In 1702, Pope Clement XI inaugurated a sundial on the floor of the church, the so-called Linea Clementina. It was designed by Francesco Bianchini, and its function was to check the validity of the new Gregorian calendar.
In 1749, major alterations were carried out by Luigi Vanvitelli in preparation for the Holy Year of 1750. Beforehand, the main entrance was on the short south-east side, which was hence the nave. Vanvitelli transferred the entrance to the long south-west side, turning the subsidiary side entrance into the main entrance. The two entrance vestibules were turned into side chapels, and the entrances blocked up by the new chapel altars. He then demolished Michelangelo's blocking wall opposite the new main entrance, and made a presbyterium out of the passageway to the nautatio. Finally, he knocked a hole in the ancient screen wall on the south-west side of the nautatio in order to add an apsidal choir.
After the unification of Italy in 1870, the Carthusians were evicted from the buildings, which for some time was used as a military barracks. It was eventually handed over to the Franciscan Order of Minims, and finally to the diocesan clergy. In 1896, the wedding of the Prince of Naples, later King Victor Emmanuel III, raised the status of the church. It has since been the scene of religious ceremonies promoted by the Italian State. The church became titular in 1906, and was given the status of minor basilica by Pope Benedict XV in 1920.