Vatican researchers have scaled the cupola on top of St Peter’s Basilica to use high-tech tools to study the dome’s innards and found the structure to be more sturdily built than experts had long believed, the Vatican’s newspaper said.

The research, conducted by two members of the basilica’s engineering and maintenance department, “does not only allow us to discover the materials and techniques used for the construction, but it allows us to learn its actual state of health”, L’Osservatore Romano wrote.

It said the research found that the 16th century equivalent of today’s reinforcement concrete was used to construct the dome, which was largely based on a design by Michelangelo.

Before the project began, researchers combed art historians’ writings, but concluded they “presented numerous inaccuracies,” since much was based on either oral tradition or on accounts that were never verified, according to L’Osservatore.

One of the researchers climbed the dome “like an Alpine mountaineer,” and, armed with geo-radar, discovered seven internal iron rings used to hold the travertine stone together, the report said.

Scholars, using centuries-old documents, had thought only two rings were used to girdle the structure, it added.

The Vatican says the dome, topped by a cross which towers 520-foot above the ground, seems to have been even more sturdily constructed than long believed.

Using techniques of the latter 16th century, the builders “used a system of reinforcement similar to modern reinforced concrete,” the researchers concluded, in L’Osservatore.

Iron chains, set at various heights, helped reinforce the stability of the cupola, to the likely relief of countless tourists who have made the dizzying climb inside the dome to admire the view from the top.

L’Osservatore said researcher Marta Carusi, scanning the dome’s walls with a geo-radar device, determined “the exact position of girdling rings, bars and chains” used to keep the dome stable.

“Hidden inside the walls, these materials weren’t able to be pinpointed and the memory of (their use in construction) had been lost,” the paper said.

The geo-radar exam, which involves electromagnetic impulses and echoes, allowed experts to find many more metallic under-pinnings than long believed, the paper said.