The Church was built by James Quarenghi (1744-1817), "one of the greatest architects in the Europe of his time" (A. M. Brizio).
It was designed in 1769 ( Quarenghi's designs are preserved in the archives) , and consecrated in 1776. "We cannot call its architectural style purely neoclassic" ( Lavagnino). "Although Quarenghi borrowed many elements from the neoclassic style, he avoided its coldness and succeeded in making a real work of art" (Brizio). "There is a certain splendour in the church and a clear, harmonious distribution of spaces… The architectural movement and the vivid harmony of spaces gives to the building a real artistic value" (V. Chirone).
In 1779 Quarenghi went to Russia where he remained for his whole life. Many of the important building in Petersburg are his: the State Bank, a Theatre, the Academy of Science,… The wooden choir was built in 1643-1644. The following paintings above the side altars are interesting: the Guardian Angel, St. Jerome, St. Andrew's martyrdom. The frescoes in the sacristy were done by Marcello of Piacenza (1578). The paintings depicting Our Lady with the Divine Child and St. Anselm ( transformed into St. Clemente) is attributed to Carlo Maratta (1625-1715).
In the sacristy there is a stairway which leads to some underground chapels. The first of these, dedicated to the Angels, has some XVth century paintings, which were unfortunately badly touched up in 1857. On the old transept of the gothic church, above the vault of the present church of Quarenghi, are some important frescoes of the XVth century. These frescoes follow the style of the school of Umbria which was so widespread in Latium in the first quarter of that century.