Evoking the more famous Christian burial grounds along Rome's Appian Way, the Catacombs of St. John contain some 20,000 ancient tombs, honeycombed tunnels of empty coffins that were long ago looted of their burial riches by plundering grave robbers.

In Roman times, Christians were not allowed to bury their dead within the city limits, so they went outside the boundaries of Syracuse to create burial chambers in what had been used by the Greeks as underground aqueducts. The early Christians recycled these into chapels. Some faded frescoes and symbols etched into stone slabs can still be seen. Syracuse has other subterranean burial grounds, but the Catacombs of St. John are the only ones open to the public.

You enter the "world of the dead" from the Chiesa di San Giovanni, now a ruin. St. Paul is said to have preached on this spot, so the early Christians venerated it as holy ground. Now overgrown, the interior of the church was abandoned in the 17th century. In its heyday, it was the cathedral of Syracuse.

The church's roots date from the 6th century, when a basilica stood here, but it was eventually destroyed by the Saracens. The Normans reconstructed it in the 12th century, but in 1693 an earthquake destroyed it. A baroque church was then built, but was left in ruins by the earthquake of 1908. All that remain are roofless Norman walls and about half of the former apse. A beautiful rose window is still visible on the facade of the Norman church.

Underneath the church is the Cripta di San Marciano (Crypt of St. Marcian), constructed on the spot where the martyr is alleged to have been beaten to death. His Greek-cross chamber is found 5m (16 ft.) below the ground.

Warning: Make sure that you exit well before closing. Two readers who entered the catacombs after 5pm were accidentally locked in.