The Basilicas of Rome are four, and they are also called the Papal Basilicas, symbol and hub of Christianity in the world: Saint Peter in the Vatican, Saint John in Laterano, Saint Paul Outside the walls, and Saint Mary Major.
All the basilicas in Rome, such as Saint Peter's, have a Papal Altar, where only the Pope can officiate at the Eucharist during the Holy Mass, the celebration of the passion and resurrection of Jesus Christ according to the Catholic Church. And all the basilicas have a Holy Door which, if crossed during a Holy Year, guarantees – according to the tradition – the plenary indulgence from the sins you have committed. Both traditions – the papal altar and the holy door – define the spiritual and artistic richness of Rome's basilicas.
Saint John in Laterano. It is the most important Christian basilica after Saint Peter's. It was built in 313 by order of the emperor Constantine. It has endured destruction and various fires; the facade we see today dates from 1734, while the interiors were renovated by Borromini, the great architect of the Baroque.
Saint Paul Fuori le Mura. Part of the UNESCO World Heritage since 1980, the Basilica hosts the body of Paul the apostle. Its construction began in 64 AD, and it was consecrated in 324. In 1823 it was burned down by a terrible fire, which nonetheless spared its splendid mosaics.
Saint Mary Major. It is the only one of the four Basilicas which has conserved its Paleochristian layout. Its origin is very ancient and along the centuries it was embellished by many works of art, and in particular by wonderful mosaics.