Dedication of the Basilica of Saint John Lateran
This is the oldest and ranks first among the four Patriarchal Churches of Rome.( St John Lateran, St Peter's, Saint Mary Major, and St Paul Outside the Walls.)
It was originally the Palace of Constantine, and was dedicated to be the church of the Pope.
The present Archbasilica was built later on the site of the original church, and is known as "Saint John Lateran", because it was dedicated to Saint John the Baptist.