Spooky subterranean chambers, installed in underground aqueducts that had been abandoned by the Greeks, contain some 20,000 ancient Christian tombs. They are entered through the Church of San Giovanni, now in ruin but holy ground for centuries; this was the city’s cathedral until the church was more or less leveled by an earthquake in 1693. St. Paul allegedly preached here when he stopped in Siracusa around a.d. 59, and a church was erected in the 6th century to commemorate the event. The Cripta di San Marciano (Crypt of St. Marcian) honors a popular Siracusan martyr, a 1st-century-a.d. bishop who was tied to a pillar and flogged to death on this spot.