Squeezing into claustrophobic tunnels on their stomachs, British archaeologists have mapped a hidden world of Roman ruins lying beneath the world’s first cathedral.

The British experts employed potholing techniques and laser instruments as they squirmed their way through shafts and chambers 30ft beneath the 17th century Basilica of St John Lateran in Rome.

The present-day basilica stands on the ruins of a 4th century AD basilica which was founded by the Emperor Constantine, who adopted Christianity as the official religion of the Roman Empire.

The basilica was in turn built on top of a huge barracks that housed a detachment of elite Roman imperial cavalry.

Beneath the barracks, archeologists explored yet another layer of Roman ruins - sumptuous villas decorated with extravagant frescoes, some of them marked with graffiti left by Roman soldiers and military engineers.