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 experts employed potholing techniques and laser instruments as they squirmed their way through shafts and chambers 9m beneath the 17th-century Basilica of St John Lateran in Rome.
The present-day basilica stands on the ruins of a 4th-century basilica 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, archaeologists 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. The legionaries recorded their names and units as they dismantled the villas, carting off marble and other materials to be re-used in the construction of the barracks.