Naples Cathedral (Il Duomo di Napoli) provides stunning examples of medieval Italian architecture.

The cathedral was founded in the fourth century. Previously, a Greek temple to Apollo had been located on the site.

A baptistry that was built at that time still remains, although it has been relocated. The dome of the baptistry is decorated with 5th century Byzantine Mosaics.

Naples Cathedral includes the 6th century Basilica di Santa Restituta, which was rebuilt in the 14th century.

Most of the cathedral that exists today was built between 1294 and 1323.

Because Naples is an earthquake-prone city, parts of Naples Cathedral have had to be rebuilt over its long history. The west facade was rebuilt in 1407 and the rest of the cathedral was rebuilt in 1456.

An earthquake resulted in the Basilica di Santa Restituta being rebuilt a second time in 1688.

Some ancient features of the basilica, including fragments of the mosaic floor, still remain. The columns of the basilica may have originally been part of the temple to Apollo.

The neo-gothic west facade of the Cathedral is the result of a renovation that took place between 1877 and 1905.

Luca Giordano painted the portraits of the 46 saints that can be found along the walls of the naves of the Cathedral. Fabrizio Santafede painted the nave's ornate ceiling.

On the right side of the nave is the chapel of San Gennaro, Naples' patron saint.

The tombs of Charles I of Anjou, who commissioned the building of the Cathedral, Charles Martel and Clementina of Habsburg, Martel's wife, are located over the nave's central doorway.

Naples Cathedral contains the reliquary of San Gennaro. The reliquary is said to contain the saint's blood and shards of his skull.

The coagulated blood is said to liquefy, miraculously, three times a year - on the first Saturday in May, on September 19 and on December 16.

On September 19, the day of the Festival of San Gennaro, the bishop brings an ampoule containing what appears to be a vile of blood near the bust of San Gennaro, waiting for it to liquefy. Thousands of pilgrims and tourists watch for the miracle. The substance usually liquefies.

The vial does contain blood, according to a test, which used light, that was performed in 1902.

However, the vial is sealed and the substance inside has never been tested. Skeptics think that the vial contains a sticky material like honey or wax that melts when the bishop's hands warm up the vial.

Sometimes the substance in the vial does not appear to liquefy. According to superstition, if the blood does not liquefy, a disaster will occur.