During construction work next to the Lateran Basilica in Rome, archaeologists have made an unexpected discovery.
They came across extensive remains of buildings that are presumably part of the old papal residence, where the successors of the Apostle Peter had their seat until the 13th century.
According to Italian media reports on Thursday, the first of the structures now discovered were built under Emperor Constantine in the fourth century.
The heavily fortified complex was renovated for the last time in the 13th century before the papacy moved to Avignon in southern France for almost a century.
Only since the return of the popes at the end of the 14th century has the Vatican been the centre of power of the Roman Church.
The old papal residence fell into disrepair and was forgotten.
"An inexhaustible treasure trove of archaeological treasures"
The excavations are taking place as part of the remodelling of the spacious square in front of the Lateran Basilica and were initiated with a view to the expected rush of pilgrims in the Holy Year 2025.
Italy's Culture Minister Gennaro Sangiuliano commented on the excavations, saying: "The new discoveries prove once again that Rome is an inexhaustible treasure trove of archaeological treasures."
The finds could contribute to opening up new knowledge about the history of the city.
The papal residence on the Lateran, known as the "patriarchal seat", was, among other things, the scene of the events of the "dark century" of the papacy, which lasted from around 890 to 1046.
At that time, Roman clans and European powers fought for influence in Rome.
Several popes were deposed, imprisoned or murdered.