When we think of the seat of Catholicism, images of St. Peter’s in Rome come to mind. In reality, the seat of Catholicism is actually the Basilica of St. John Lateran in Rome because this is the official church that the pope presides in as bishop of Rome. It is this capacity — the bishop of Rome — that makes the pope head of all bishops. Thus it is this church, where the pope presides, that stands as the mother of all churches around the world.
This church was the first one built after Constantine ceased the persecution of Christians in 313. For years, the Laterni family held the land where the church now stands, which gives the basilica its name. The basilica was dedicated in 324 and that is where popes lived and presided until the 1300s. Four ecumenical councils of the magnitude of Vatican II were held there.
The basilica was originally dedicated under the name of Most Holy Savior, but in the sixth century took on the names of John the Baptist and John the Evangelist. Now it is known as the Basilica of St. John Lateran, which rolls all of this history together.