Today is the feast of the dedication of the Lateran or as it is known by its official title The Archbasilica of the Most Holy Savior and Saints John the Baptist and the Evangelist at the Lateran. The Lateran is the mother church of the whole inhabited world. It is the cathedral of Rome. And while many believe, erroneously, that St. Peter is the Holy Father's cathedral, that honor goes to the Lateran. It was built by the Emperor Constantine during the pontificate of Sylvester I, and dedicated on this day in the Year of Our Lord 324. It is the oldest of the four major basilicas of Rome.
The actually patron of the church is not either of the St. Johns, but rather the Most Holy Savior himself, Jesus the Christ.
The basilica itself has been rebuilt many times over the ages. All four the Rome's major basilicas are assigned archpriests, who are usually cardinals. Agostino Vallin, who is also Vicar of Rome is the current Lateran archpriest.