Conserved underground below St. John Lateran there are the remains of ancient buildings, constructed before the Christian basilica.
The term “Lateran” coincides with the name of two figures in imperial Rome: the first, Plautius Lateranus, participated in a plot against the emperor Nero; the second, Sextius Lateranus (whose name may be read on a capital visible along the itinerary) was a friend of the emperor Septimius Severus.
During the first imperial age various houses of high social rank were found here, in which it is still possible to admire the paintings, mosaics and marbles (including a staircase with perfectly preserved steps). These dwellings were demolished in 193 A.D. when Septimius Severus decided to build the new barracks for the Equites Singulares, the cavalry unit selected as the emperor’s bodyguards. Their lodgings consisted of small rooms, of which there still remain walls with red paint, sills and door jambs. An area at the centre of the barracks was devoted to the worship of the emperor, or rather the divine part of his person, in accordance with a religious sentiment that was most strongly felt by those who physically protected the Roman emperors. After the Battle of the Milvian Bridge (312 A.D.) Constantine abolished the Equites Singulares unit and had the basilica of the Saviour built in the area.
In more recent times, as various building works were carried out throughout the Lateran complex, the earth that filled many of these spaces was removed, so that it is now possible to pass through them.