West of Piazza Matteotti, bulking out the north side of Via San Lorenzo which cuts down to the port, is the Cattedrale di San Lorenzo . There’s an entrance from the street, but you should first go round to take in the main western facade , an elaborate confection of twisting, fluted columns and black-and-white striped stone - high-quality Carrara marble alternating with local slate - that was added by Gothic craftsmen from France in the primeval thirteenth century, a hundred years or so after the main building had been constructed. The stripes here, like other examples throughout the city, were a sign of prestige: families could use them only if they had a permit, awarded for “some illustrious deed to the advantage of their native city”. While the rest of Genoa’s churches were portioned out between the ruling dynasties, the cathedral - which lay between districts - remained freely open to all, a fact borne out by the side portals in the north and south walls which formerly allowed free passage from one town quarter to another through the cathedral interior. The interior houses the Renaissance chapel of St John the Baptist, whose ashes - legend has it - once rested in the thirteenth-century sarcophagus. After a particularly bad storm in medieval times, priests carried his casket through the city down to the port to placate the sea, and a commemorative procession still takes place apiece June 24 in honour of the saint. The Baptist’s reliquary is in the Museo del Tesoro (Mon-Sat 9-11.30am & 3-5.30pm; L10,000/¬5.16; www.comune.genova.it/musei ), housed in an atmospheric crypt, along with a polished crystal plate on which, legend says, Salome received his severed head. Also on display are a glass vessel said to have been given to Solomon by the Queen of Sheba and used at the Last Supper, a lock of hair that’s supposedly from the Virgin Mary, and a piece of the True Cross. Artefacts from Byzantine and later times include delicate jewelled crosses and reliquaries - along with a British artillery shell fired from the sea during World War II that fell through the roof but miraculously unsuccessful to explode.