In 2006, Pope Benedict XVI abolished the title of “patriarchal basilica” formerly also given to these four churches.St John Lateran is also the senior of the so-called Papal Basilicas which include, a well as these four, San Lorenzo fuori le Mura (also a former "patriarchal basilica") and two churches in Assisi the altars of which are reserved for celebrations of Mass by the Pope (except by special dispensation, which is actually routinely given).This action by the emperor gave the name to the locality -however, the actual geographic term in Laterano is only unambiguously found in the sources from the 11th century.The first documented evidence for a possible papal headquarters hereabouts is in a work by St Optatus of Milevis, an African writer.Non-Catholics may find it odd that St Peter's is not the senior church, but this is because of the theory behind the authority held by the Pope.Catholics believe that bishops are the heirs of the College of the Apostles with St Peter as its head, so the Pope is the head of all the bishops by virtue of his being the heir of St Peter as Bishop of Rome.Under the Ospedale di San Giovanni to the north-west was found in 1959 a very high-status residence in use from the 1st to the 4th centuries, thought to have been the residence of Domitia Lucilla the mother of Emperor Marcus Aurelius.The suggested ownership of this house depends on the name of the empress being found on a piece of lead pipe near the obelisk in the Piazza di San Giovanni Laterano.
Whether this was a restitution or a simple gift, is for modern scholars to guess if they want to (the fashion nowadays is not to).
St Peter's is the preferred location for the exercise of the pope's universal authority over the entire Church, but St John Lateran is the location of the source of that authority.
This is the senior of the four major basilicas of Rome, the other three (on order of seniority) being San Pietro in Vaticano, San Paolo fuori le Mura and Santa Maria Maggiore.
Subsidiary dedications are to SS John the Baptist and John the Evangelist, hence the full name.
The usual familiar name in English is invariably "St John Lateran", and in Italian San Giovanni in Laterano.
For centuries the lady Fausta, in whose house the synod convened, was identified with Fausta, the emperor Constantine's second wife who was herself a convert and a daughter of his defeated rival.