Although this church existed for over fourteen centuries before the creation of the United States, Americans can in some sense claim it as our own, as it has been the home of our national parish in Rome since 1922. The importance of this site to Christians can be traced to the late third century, during the reign of Diocletian. This emperor, whose name is well known for the persecutions under him, desired to marry his relative, Susanna, to one of his co-emperors in a political marriage. Susanna did not wish to be part of this, not only because of her Faith but also because she had taken a private vow of virginity. When Diocletian found out about this, he ordered the punishment not only of her but also of her father, Gabinus, and three Christian uncles, one of whom was Pope Gaius. Susanna received the crown of martyrdom immediately, with her father dying in prison and her uncles and some other relatives being executed outside the city. Pope Gaius escaped these persecutions, returning to continue leading the Church in the city.
During these times, the house of Gaius, standing on this spot, was used as a house church and was later a titulus under his name. In the early fourth century, a basilica stood on this site. Although possibly used for secular purposes at first, it was certainly used solely for Christian worship by 330. This first structure had the shape common to most early churches, with two aisles on either side of a nave, which terminated in an apse. At this time the church was referred to as St. Gaius, only becoming known by the name of St. Susanna at the turn of the seventh century, due to the popularity of her cult. A renovation was undertaken at the turn of the ninth century, followed by another one in the eleventh. However, as with many old churches in the city the long centuries took their toll on the structure, and in the late fifteenth century Sixtus IV directed a renovation which removed the aisles to strengthen the building, reducing it to a single nave. A section of each aisle were retained and transformed into a side chapel. The interior decoration undertaken in the late sixteenth and early seventeenth centuries is that which we see today. Also from this period is the façade, completed in 1603. Designed by Carlo Maderno, it was thought so beautiful when completed that the architect was soon after given the commission of the façade for the new St. Peter’s Basilica.