In addition to being the pope's cathedral, it also has a special connection to various popes in the history of the Church who chose the name Leo.
One of the oldest churches in Rome is St. John Lateran, given to the Bishop of Rome by Emperor Constantine in the 4th century.
Ever since, it has remained the "pope's cathedral," the place where the pope has his official seat or chair, and where historically the popes used to live.
In this way St. John Lateran has a connection to all the popes throughout history, but it also has had a special place in the lives of popes with the name Leo.
Pope St. Leo the Great
During the 5th century, a large invading army of Vandals pressed into the city of Rome. Unlike with the army of Attila the Hun, Pope Leo the Great was unable to convince them to turn back entirely.
Benedict XVI narrates in his general audience, "Unfortunately, the outcome of another Papal initiative three years later was not as successful, yet it was a sign of courage that still amazes us: in the spring of 455 Leo did not manage to prevent Genseric's Vandals, who had reached the gates of Rome, from invading the undefended city that they plundered for two weeks. This gesture of the Pope - who, defenseless and surrounded by his clergy, went forth to meet the invader to implore him to desist - nevertheless prevented Rome from being burned and assured that the Basilicas of St. Peter, St. Paul and St. John, in which part of the terrified population sought refuge, were spared."
While St. John Lateran was spared from being burnt down, it wasn't spared from looting. The Catholic Encyclopedia explains, "This splendor drew upon it the attack of the Vandals, who stripped it of all its treasures. St. Leo the Great restored it about 460."
Thus, St. Leo the Great had a hand in preserving and restoring St. John Lateran for future generations.
Pope Leo III
Pope Leo III is known for building banquet halls at the Lateran Palace (which was connected to St. John Lateran). They were called the the Triclinium of Pope Leo III and while these halls are no longer in existence, there is a mosaic in Rome that commemorates it.
The mosaic features St. Peter giving the pallium to Pope Leo III.
Pope Leo XIII
Prior to Pope Francis, Pope Leo XIII was the last pope to have been buried outside of St. Peter's Basilica. He chose as his resting spot St. John Lateran.
