Santa Susanna is an 15th century monastic and titular church. It is on the Piazza San Bernardo, on the Via XX Settembre. The dedication is to St Susanna, and the full official title is Santa Susanna alle Terme di Diocleziano.
For reference, a plan of the church is available
here.
The first Christian place of worship was built here in the 4th century. It was probably the titulus of
Pope Caius (283-296) - the tituli were the first parish churches in Rome. Caius was Santa Susanna's uncle, and tradition claims that the church stands on the site of her martyrdom.
A church was built in 330, and named San Caio after the owner of the first chapel. In 590, the church was rededicated to Santa Susanna because of her growing popularity.
Pope Leo III (795-816) had the church redecorated.
It is mentioned in the Catalogue of Turin as a titular church for a presbyterial cardinal. It was served by 6 clerics at the time.
It was rebuilt under
Pope Sixtus IV (1471-1484), and again by
Girolamo Cardinal Rusticucci between 1593 and 1603. The architect was
Carlo Maderno.
In 1587,
Pope Sixtus V (1585-1590) gave the church and an adjacent building to the Cistercian nuns.
From 1922 (de facto; formally since 1924) until 2017 it was the national church of the USA.
In the crypt are the remains of a 3rd century house, which may have been Susanna's home.
