Royal Chapel of the Treasure of San Gennaro

Three times a year, the people of Naples wait to see whether a dried relic, venerated as the blood of Saint Januarius, the city's patron, will turn liquid again. The two glass ampoules are kept in this chapel inside Naples Cathedral, in a safe behind the altar. The chapel stands within the cathedral, yet it belongs to the Deputation, a lay body that has represented the city since Naples vowed a new chapel to its saint in January 1527, praying for an end to plague and war.

Building began only in 1608, to a Greek-cross plan by the architect Francesco Grimaldi, and the chapel was completed in 1646. The painter Domenichino, called down from Rome, frescoed the vaults and painted large altarpieces on copper, but he died in Naples in 1641 with the work unfinished. Giovanni Lanfranco, his long-time rival, then painted the dome as a spiral of saints rising into paradise.

The last great altarpiece came from Jusepe de Ribera, the Spanish painter who made his career in Naples. Painted on a copper sheet more than three metres tall, it shows Januarius walking out of a furnace unharmed, one of the miracles told of him. Next door, the Treasure Museum displays gifts made to the saint over the centuries, including a jewelled mitre made in 1713 and set with thousands of precious stones.