The island of Torcello, located about 10 km north of Venice, was once a center of power in the Venetian Lagoon. Its main structure is its cathedral, the Basilica of Santa Maria Assunta, which dates back to the 7th century.
It was built on behalf the Byzantine Exarch of Ravenna following the transferral of the episcopal seat of Altino to Torcello, to escape the Lombard invasions on the mainland. During this early period, it was also one of the most important trading centers. Parallel to the development of the episcopal seat, the island enjoyed a period of splendor becoming one of the major centers in the lagoon. Thanks to the lagoon’s salt marshes, the salt became Torcello’s economic backbone and its harbor developed quickly into an important trade center involved in Byzantine and Eastern Mediterranean commerce. Later, though, the arrival of the plague and expanding swamps forced its inhabitants to flee to surrounding islands. After being expanded for the first time in 826 A.D. and rebuilt in 1008, when it was finally consecrated to Santa Maria Assunta, Torcello's Basilica anticipates some of the characteristics that were fully developed at a later stage inside the best known building in Venice – St Mark’s Cathedral. Despite the state of neglect affecting Torcello starting from the 14th century, Santa Maria Assunta retained its function as a cathedral until 1818, when it was downgraded to a parish church under the Venice Patriarch.
Torcello Cathedral (the Basilica of Santa Maria Assunta) represents a significant example of Venetian Byzantine architecture – a building with a basilica design divided by Greek marble columns  – with beautifully decorated capitals – in three naves: a very high central one and two smaller lateral ones. The main subject of the decorations of the Torcello Cathedral is the Virgin Mary, who welcomes visitors from the top on entering the cathedral, in an extraordinary mosaic on a golden background located in the bowl of the main apse. The Virgin Mary is wrapped in precious garments and is holding Jesus in her arms, whilst on a lower level are the Apostles, depicted in front position and identified by inscriptions.
The most important mosaic of Torcello Cathedral is the Last Judgment, an impressive representation built between the 12th and 13th centuries and occupying the entire counter façade of the church. This mosaic can be compared to a page from the Apocalypses: from the crucifixion between the Virgin Mary and St John to the ascent of the Limbo, where Christ frees and judges the souls of humans sitting amongst the Virgin Mary, St John and the Saints. On the lower levels is a depiction of the separation of the blessed from the damned: the latter are inflicted the punishments of the law of retaliation due to their capital vices. There are stunning analogies with the Divine Comedy, had it not been the case that Dante wrote his oeuvre around a century after the completion of this sumptuous masterpiece. The crypt is a passage underneath the altar from where it is possible to admire the ancient brickwork of the mediaeval basilica, whilst the sacristy enshrines the ancient porch of Santa Maria Assunta, which was closed off at later stage to create a fourth nave. In the sacristy it is possible to admire several stone elements dating back to the 9th century and a mysterious Roman sarcophagus, hidden behind a secret passageway which the legend claims it housed, for some time, the body of Mark the Evangelist.