In 1561 Pope Pius IV (r. 1559-65) commissioned Michelangelo (1475-1564), by then in his eighties, to convert the ruins of the ancient Baths of Diocletian into the church of Santa Maria degli Angeli e dei Martiri. It was to be the master's last architectural work.
The cavernous body of the church is 90 m long, 27 m wide and 28 m high. The eight colossal monolithic columns, nearly 14 m high, are ancient Roman and made of granite; the rest of the columns in the church are made of brick and plaster and painted to look like granite!
Embedded in the floor is a meridian, the work of Francesco Bianchini, which was inaugurated by Pope Clement XI (r. 1700-20) on October 6th, 1702. It served to regulate the city's clocks until 1846.
In the middle of the 18th century, Santa Maria degli Angeli was radically restructured by Luigi Vanvitelli (1700-73), the Neapolitan architect and engineer. Vanvitelli altered the orientation of the church, moving the entrance and turning the nave into a colossal transept. He also built the choir and apse on the north east side. (Pope Pius IV is buried in a pavement tomb in the choir.)
The entrance incorporates all that is left of the caldarium (hot room). The beautiful bronze doors (2005) are the work of the Polish sculptor Igor Mitoraj (1944-2014), who also carved the marble head of St John the Baptist inside the church.
The circular vestibule stands on the site of the tepidarium. On the right is the tomb of the painter Carlo Maratta (1625-1713), which he designed himself; the bust (c. 1704) is by Francesco Maratta. On the left is the tomb of Salvator Rosa (1615-73); the sculpture is by Bernadino Fioriti. The statue of St Bruno, founder of the Carthusian Order, is by the French sculptor Jean-Antoine Houdon (1741-1828).
In addition to the creation of the church, Pope Pius IV also had part of the ruins of the Baths of Diocletian converted into a Carthusian monastery. The design of its beautiful Chiostro Grande (Great Cloister) is ascribed to Michelangelo.