Constantine built the original St. Peter's Basilica, And Also Built The "Lateran patriarchate" where the Popes have resided.
Constantine is the foundation and father of Roman Catholicism the State Church, a (Fact)
Wikipedia: St. Peter's Basilica
Old St. Peter's Basilica was the 4th-century church begun by the
Emperor Constantine the Great between 319 and 333 AD.
[26] It was of typical basilical form, a wide nave and two aisles on each side and an apsidal end, with the addition of a
transept or
bema, giving the building the shape of a
tau cross. It was over 103.6 metres (340 ft) long, and the entrance was preceded by a large colonnaded
atrium. This church had been built over the small shrine believed to mark the burial place of
St. Peter, though
the tomb was "smashed" in 846 AD.
[27] It contained a very large number of burials and memorials, including those of most of the popes from St. Peter to the 15th century. Like all of the earliest churches in Rome, both this church and its successor had the entrance to the east and the apse at the west end of the building.
[28] Since the construction of the current basilica, the name
Old St. Peter's Basilica has been used for its predecessor to distinguish the two buildings.
Wikipedia: Lateran Palace
The
Domus Laterani came into the possession of the emperor when
Constantine I married his second wife
Fausta, sister of
Maxentius. Around 312, Constantine had razed the imperial horse-guards barracks adjoining the palace, which was known as
Domus Faustae or "House of Fausta" by this time; the
equites singulares Augusti had supported Maxentius against Constantine. He commissioned the construction of the
Basilica di San Giovanni in Laterano on the site.
[2] The
Domus was eventually given to the Bishop of Rome by Constantine.
As Byzantium grew less able to help prevent
Lombard incursions, the papacy became more independent of the Empire. Prior to the early eighth century, the residence of the bishops of Rome was not called a palace, but rather the "Lateran patriarchate".
[3] The incentive to refurbish the Lateran patriarchate as a true palace was to create an imperial residence from which the pope could exercise not only spiritual but also temporal authority.