Archeological investigations carried out over a 70-year period (at the beginning of the 20th century) by the Studium Biblicum Franciscanum (Jerusalem) revealed an octagonal mid-5th-century ecclesiastical structure built around an earlier one-room dwelling dated to the 1st century CE. The central octagonal shrine, enclosing a dry-wall basalt structure, was surrounded by an octagonal ambulatory similar to the ambulatory in the Rotunda of the Holy Sepulcher in Jerusalem; or the later octagonal Islamic shrine built on the Haram esh-Sharif (the Temple Mount).
The room contained within the central octagonal shrine appears to have been part of an insula (a complex of small single-storey residential rooms and courtyards) that toward the end of the 1st century was put to public use, possibly as a domus ecclesia, a private house used as a church. The plastered walls of the enshrined room were found to be scratched with graffiti in Aramaic, Greek, Syriac and Latin, containing the words "Jesus", "Lord", "Christ" and "Peter".
The enshrined room is presumed to be the "House of Simon, called Peter" reported by the Spanish pilgrim, the Lady Egeria, who visited the town sometime between 381-384 during her pilgrimage to the Holy Land. She described in some detail how the house of "the prince of Apostles" had been made into a church, with its original walls still standing.
In the mid-5th century, this room was enshrined within an octagonal-shaped building. This was the church later described by the 6th-century Piacenza Pilgrim who wrote, "The house of St. Peter is now a basilica." Like the nearby synagogue, the octagonal-shaped church was destroyed early in the 7th century, possibly at the time of the Persian invasion.
The present Franciscan church was built in 1990 over the site of the Insula Sacra to preserve the archeological finds and to permit visitors and worshippers an overview of the various architectural elements.
Sources: Israeli Foreign Ministry