The Santa Maria degli Angeli e dei Martiri, also known as Santa Maria degli Angeli, is an ancient Roman bath converted into a church in the 16th century. It was designed by Michelangelo.
It is located on the Piazza della Repubblica, not far from the Termini train station.
The site originally held the largest public baths in the city and were completed in 306. However, over time these baths fell into ruin. It was not until 1533 when a Cardinal acquired the site that it was used again, this time to grow gardens amongst the ruins.
By 1563 work had been start on converting the baths to the church that Michelangelo had designed. Over time alternations have been done to the church including in 1702 when a sundial was placed on the floor. The sundial was important as its function was to check the validity of the new Gregorian calendar. The validity of the calendar was important in relation to the Spring Equinox, since the date of Easter depended on it.
The modern church is well worth visiting and includes remnants of the baths. If you visit, give yourself at least 1 hour to 1.5 hours so as not to be rushed.