At the time of imperial Rome, the luxurious dwellings of the Lateran family stood here: they were a powerful Roman family whose existence is shown by Tacitus (Ann. XV 48-53-60) who mentions a Plautius Lateranus among the people involved in the Pisoni plot against Nero (66 A.D.). History has it that after the death sentence was passed on Plautius, his house was confiscated and was returned to the family one and a half centuries later, to be confiscated again soon after for reasons not related to us.
At the beginning of the 4th century the buildings were known as Domus Faustae in Lateran and according to Optatus, Bishop of Mileto, the Council called by Pope Milziade and by Constantine in 313 to solve the donatist question, assembled here. Fausta had married Constantine in 307 but in 326 she was accused of incest by her husband and sentenced to death. This accusation, though, appeared unfounded. After the departure of St. Helen for the East in 326, the palaces remained empty. It is therefore reasonable to assume that after this date (and not after 310, as stated by some writers) the building of  the basilica was started: a Christian chapel may well have stood within the Imperial palaces.The present basilica has kept to the original perimeter and foundations and the latter enclose part of the «Domus Faustae»: this was partially demolished to make room for the grandiose basilica which Constantine decided to have built within the frame of his far seeing plan (both political and religious) of new improved sacred buildings in the Rome which would soon have to relinquish to Constantinople the prestige of being the seat of Imperial power.
The Liber Pontificalis in the life of Pope St. Sylvester (314-335) proves Constantine's work. The excavations carried out at the end of the 16th century, during the last century and the most recent ones have brought to light more and more remains of the Imperial buildings. The work including the nearby Baptistery proceeded until the middle of the 4th century and Constantine, who was not to see its completion, endowed the Basilica and the Baptistery with splendid gifts.
At first dedicated to the Savior and called Lateran or Constantinian or Aurea, it was dedicated in the times of St. Gregory the Great (590-604) to St. John the Baptist and St. John the Evangelist and named after each of these Saints.The Palaces near the Basilica forming the so called «Patriarchio Lateranense» were for many centuries the residence of the Popes and for this reason the whole area was considered for a long time the symbol and the centre of the spiritual and temporal reign of the Roman Pontiffs.
The first certain events relating to the Basilica are invasions and plunders, especially those (455) made by Genseric's Vandals: their name is enough to make us realize what must have happened when their fury was let loose: the devastations lasted 14 days.St. Leo the Great (440-461) had to restore the walls and to renew the furnishings: he most likely laid the foundations of the Leonine Portico.