With its Byzantine domes and 8500 sq metres of luminous mosaics, Venice's basilica is an unforgettable sight. It dates to the 9th century when, according to legend, two merchants smuggled the corpse of St Mark out of Egypt in a barrel of pork fat. When the original burnt down in 932 Venice rebuilt the basilica in its own cosmopolitan image, with Byzantine domes, a Greek cross layout and walls clad in marbles from Syria, Egypt and Palestine.

The front of the basilica ripples and crests like a wave, its five niched portals capped with shimmering mosaics and frothy stonework arches. In the far-left portal, lunette mosaics dating from 1270 show St Mark’s stolen body arriving at the basilica. Grand entrances are made through the central portal, under an ornate triple arch with Egyptian purple porphyry columns and 13th- to 14th-century reliefs of vines, virtues and astrological signs.

Blinking is natural upon your first glimpse of the basilica's glittering mosaics, many made with 24-carat gold leaf fused onto the back of the glass to represent divine light. Just inside the vestibule are the basilica's oldest mosaics: Apostles with the Madonna, standing sentry by the main door for more than 950 years. Mystical transfusions occur in the Dome of the Holy Spirit, where a dove’s blood streams onto the heads of saints. In the central 13th-century Cupola of the Ascension, angels swirl overhead while dreamy-eyed St Mark rests on the pendentive. Scenes from St Mark’s life unfold over the main altar, in vaults flanking the Dome of the Prophets.

The latter is best seen from the Pala d’Oro, a gold altarpiece studded with 2000 emeralds, amethysts, sapphires, rubies, pearls and other gemstones. It houses the sarcophagus of St Mark's and is guarded by wide-eyed saints in vibrant cloisonné, begun in Constantinople in AD 976 and elaborated by Venetian goldsmiths in 1209. Other holy bones and booty from the Crusades fill the Tesoro; while ducal treasures on show in the museum would put a king’s ransom to shame. A highlight is the Quadriga of St Mark's, a group of four bronze horses originally plundered from Constantinople and later carted off to Paris by Napoleon before being returned to the basilica and installed in the 1st-floor gallery. Portals lead from the gallery on to the Loggia dei Cavalli, where reproductions of the horses gallop off the balcony over Piazza San Marco.

The roped-off circuit of the church interior is free and takes about 15 minutes. For entry, dress modestly (ie knees and shoulders covered) and leave large bags around the corner at Ateneo di San Basso's free one-hour baggage storage (10am to 4.30pm).

Between mid-September and October, the diocese offers free guided tours at 11.30am Monday to Friday explaining, in various languages, the theological messages in the mosaics. Reservations (041 241 38 17) are essential.