The "Arcibasilica di San Giovanni in Laterano" (Archbasilica of Saint John Lateran) is the Cathedral of the Diocese of Rome, and serves as the seat of the bishop of Rome, the pope. It is the only "archbasilica" in the world, and as a property of the Holy See, the archbasilica and its adjoining edifices enjoy an extraterritorial status from Italy.
Founded in 324 AD, it is the oldest public church in the city of Rome, and the oldest basilica of the Western world. Behind the main altar, it houses the cathedra of the Roman bishop.
the church burned downs a few times and it was reconstructed / enlarged / restored several times through the centuries. This results in a mix of styles, from Gothic to Baroque, Rococo, Neo-classical. 22 Popes are buried in this church.
From the church you can access the Lateran Cloister (reviewed separately) and the Lateran Treasure.
The Lateran Treasure includes sacred objects and vestments from the 11th to the 20th century.
While the entrance to the church is free, you have to pay to visit both the cloister and the treasure (one ticket for each).