In the liturgical calendar of the Roman Catholic Church, 9 November is kept as the Feast of the Dedication of the Lateran Basilica.
The Archbasilica of the Most Holy Saviour and Saints John the Baptist and John the Evangelist at the Lateran, to give the Basilica its full name, is one of the four major papal basilicas in Rome, and is the cathedral church of the Diocese of Rome. It is for this latter role that the Feast of the Dedication is incorporated in the liturgical calendar of the Latin Church.
In every diocese around the world, the anniversary of the dedication of the cathedral church is commemorated each year because of the significance of the cathedral church as the ‘mother church’ of that particular diocese. For the same reason, the anniversary of the dedication of the cathedral church of the Diocese of Rome is kept each year because of the building’s significance within the diocese that is the focus of church unity.