ARCHAEOLOGISTS have unearthed ruins from a hidden ancient palace which housed popes for centuries before the Vatican was established.

The discoveries give a rare glimpse into the dangers faced by the papacy in Rome’s medieval times.

Archaeologists stumbled upon complex architecture beneath the square outside the Archbasilica of St. John Lateran in Rome while making renovations for Jubilee 2025 (the Catholic Holy Year).

They unearthed large walled structures made of volcanic rock bricks, known as tuff, that date back to the 9th through the 13th centuries AD.

Some of these bricks had been reused from earlier buildings, and signs of restoration were visible in some of the walls.

This structure is believed to be part of the Patriarchio – the ancient palace which served as the popes’ official residence from the 4th century until the early 14th century.

This monumental basilica was designed by Emperor Constantine in the 4th century after the famous Edict of Milan (313 AD) legalised Christianity in the Roman Empire.

The palace complex was expanded and renovated during the Middle Ages, according to the Italian Ministry of Culture.

These walled structures are said to have acted as a defensive barrier, shielding the papacy from power struggles among Rome’s aristocratic families and raids by Saracens.

The Italian ministry said: “The construction of the structure just described took place during a long period in which Rome was the object of the raids of the Saracens, and inside it there were continuous struggles, sometimes violent, between the aristocratic families.”

‘Saracens’ was the term used for various Arab groups that launched coastal raids in Italy during the 9th and 10th centuries and later clashed with European armies during the Crusades.

“Hence the hypothesis that this mighty wall, also due to its shape, functioned as a defensive wall around the Basilica’s complex and its annexed buildings,” the ministry explained.

It said this discovery is “of extraordinary importance” to Rome’s history, as these are the most extensive excavations to have taken place in the square.

Gennaro Sangiuliano, the Italian Minister of Culture, said: “The discoveries of Piazza San Giovanni in Laterano are yet another demonstration of the richness of the territory of Rome, an inexhaustible mine of archaeological treasures.”

He added: “Every single stone speaks to us and tells its story: thanks to these important finds, archaeologists will be able to know more about our past.

The Vatican officially became the permanent papal seat in 1377.

This was after Pope Gregory XI moved the papacy back to Rome from Avignon, France, where it had been located for nearly 70 years.

From thereon, a defensive structure was no longer necessary in Rome and the area was abandoned.

This discovery coincides with Cardinal Robert Prevost’s election as the new leader of the Catholic Church – making him the first-ever American pope.

The new pope stepped out onto the balcony of St. Peter’s Basilica in the Vatican on Thursday to greet cheering crowds.

Prevost was born in Chicago in 1955 to immigrant parents of French, Italian and Spanish descent.

After graduating from Villanova University in Pennsylvania with a degree in maths, the future pontiff joined the Order of St. Augustine, taking his vows in 1978.

Ordained as a priest in 1982, he joined a mission in Peru where he spent many years leading a seminary.

While he is seen as more traditional than Francis, he is not the conservative hardliner that some in the church had hoped for after his predecessor’s efforts to make the faith more progressive.