The first St Mark’s was a building next to the Doge’s Palace, ordered by the doge in 828, when Venetian merchants stole the supposed relics of Mark the Evangelist from Alexandria, and completed by 832; from the same century dates the first St Mark’s Campanile (bell tower). The church was burned in a rebellion in 976, when the populace locked Pietro IV Candiano inside to kill him, and restored or rebuilt in 978.
Nothing certain is known of the form of these early churches. From perhaps 1063 the present basilica was constructed. The consecration is variously recorded as being in 1084-5, 1093 (the date most often taken), 1102 and 1117, probably reflecting a series of consecrations of different parts.
In 1094 the supposed body of Saint Mark was rediscovered in a pillar by Vitale Faliero, doge at the time. The building also incorporates a low tower (now housing St Mark’s Treasure), believed by some to have been part of the original Doge’s Palace. The Pala d’Oro ordered from Constantinople was installed on the high altar in 1105. In 1106 the church, and especially its mosaics, were damaged by a serious fire in that part of the city; it is not entirely clear whether any surviving mosaics in the interior predate this, though there is some 11th-century work surviving in the main porch. The main features of the present structure were all in place by then, except for the narthex or porch, and the facade.
The basic shape of the church has a mixture of Italian and Byzantine features, notably “the treatment of the eastern arm as the termination of a basilican building with main apse and two side chapels rather than as an equal arm of a truly centralized structure”. In the first half of the 13th century the narthex and the new facade were constructed, most of the mosaics were completed and the domes were covered with second much higher domes of lead-covered wood in order to blend in with the Gothic architecture of the redesigned Doge’s Palace.
The basic structure of the building has not been much altered. Its decoration has changed greatly over time, though the overall impression of the interior with a dazzling display of gold ground mosaics on all ceilings and upper walls remains the same. The succeeding centuries, especially the period after the Venetian-led conquest of Constantinople in the Fourth Crusade of 1204 and the fourteenth century, all contributed to its adornment, with many elements being spolia brought in from ancient or Byzantine buildings, such as mosaics, columns, capitals, or friezes. Gradually, the exterior brickwork became covered with marble cladding and carvings, some much older than the building itself, such as the statue of the Four Tetrarchs
The latest structural additions include the closing-off of the Baptistery and St Isidor’s Chapel (1300s), the carvings on the upper facade and the Sacristy (1400s), and the closing-off of the Zen Chapel (1500s).