The feast of the Dedication of the Basilica of St John Lateran is celebrated by the entire Church. It marks the dedication of the cathedral church of Rome by Pope Sylvester I in 324. This church is the cathedra (or chair) of the bishop of Rome, who is the Pope. A Latin inscription in the Church reads: “omnium ecclesiarum Urbis et Orbis mater et caput.” Translated, this means, “The mother and head of all churches of the city and of the world.”
The basilica was originally named the Archbasilica of the Most Holy Saviour. However, it is called St John Lateran because it was built on property donated to the Church by the Laterani family, and because the monks from the monastery of St John the Baptist and St John the Divine served it. – CNA