San Cassiano (English: Church of Saint Cassian) is a 14th-century Roman Catholic church located in the San Polo sestiere of the Italian city of Venice. A church has stood on the site since 726 with the present building dedicated to Saint Cassian of Imola being consecrated in 1376 and re-modelled during the 17th century. It has a plain exterior with several adjacent buildings overlapping it. Its interior however is richly decorated in a Baroque style.

The church is located on the Campo San Cassiano, site of the world's first public opera house, west of the Rialto Bridge and is open to visitors Tuesday-Saturday mornings.

The church houses three paintings by the Italian artist Tintoretto, including The Crucifixion of Christ painted in 1568 which the art critic John Ruskin described as, "the finest [example of a Crucifixion painting] in Europe". However, the most famous painting associated with the church is paradoxically one which is no longer there. The San Cassiano altarpiece, painted for this church by Antonello da Messina, was the first major example of oil painting in the city. It disappeared from the church in the 17th century and was cut into sections; the remaining known pieces are re-united in Vienna.

The earliest church on this site was built in 726 and dedicated to Saint Cecilia, the patron saint of musicians and music. Over the centuries there have been several reconstruction projects, including one following a fire in 1106, and a major rebuild which commenced in 1350. This building was consecrated in 1376 and re-modelled in the early 17th century to give it its current appearance which dates from 1663. A large campanile, 43 metres (141 ft) high, was added to the church in the 13th century, though its rugged style suggests that it may have been a guard tower which was acquired by the church.

In 1509, the funeral procession of Catherine Cornaro, the former queen of Cyprus and wealthy Venetian noblewoman, began at San Cassiano. From here it crossed a floating bridge to the church of Santi Apostoli where she was buried in the Cornaro family chapel.

The church has a 13th-century campanile which was modified shortly after with the addition of a Gothic belfry. On the side facing the water is a door which formerly had a porch (portico), a feature which was demolished in the 19th century. The church is typically described as having the appearance of a "big box" with buildings close by and overlapping on several sides. Unlike many churches in Venice it has no facade and overall the exterior is plain and unadorned. A feature which may possibly have been retained from the original church is the door jambs or doorposts, which date back to the Byzantine era. Entry to the church is usually through a side door in the wall facing the Campo San Cassiano.

In contrast to the plain exterior, the church's interior is highly decorated in the Baroque style. It has an altar by Heinrich Meyring and Nardo. Meyring is notable for the large altar he produced for the church of San Moisè, also in Venice. The ceiling of the church was painted by Costantino Cedini, a student of Giambattista Tiepolo, and has recently been restored. In 1746 Abbot Carlo del Medico commissioned a chapel which is located on the left-hand side of the church. It contains an altarpiece dating to 1763 and a ceiling fresco, both by the artist Giambattista Pittoni. The renowned playwright Count Carlo Gozzi was buried in this church, although his tombstone has not survived.

• 
  Interior
• 
  Ceiling by Costantino Cedini.
• 
  Organ

The chancel of San Cassiano houses three paintings by Tintoretto who was a former parishioner of the church. These are The Resurrection, The Descent into Limbo and The Crucifixion, all of which were completed between 1565 and 1568. The art critic John Ruskin described the latter as, "the finest [example of a Crucifixion painting] in Europe" and noted its particularly interesting perspective which Ruskin said gave the viewer the impression that they were "lying full length on the grass, or rather among the brambles and luxuriant weeds". Tintoretto's Resurrection was painted in defiance of the Council of Trent's demand that all depictions of the resurrection feature a standing, rather than hovering, Christ figure.

The Sicilian artist Antonello da Messina was commissioned by Pietro Bon to paint an altarpiece for the church. Completed between 1475 and 1476, his Sacra Conversazione was one of the earliest appearances of oil in the city's artworks. It brought a style of altarpiece that would be imitated by other Venetian artists such as Giovanni Bellini, Giorgione and the Vivarini brothers, Antonio and Bartolomeo, establishing a template that would be used all the way through to Titian. San Cassiano's altarpiece disappeared from the church sometime during the 17th century and reappeared in the private collection of the Austrian Archduke Leopold William where it was attributed to Giovanni Bellini. After being removed from Venice the altarpiece was split into a number of fragments. Only three of these were found and these are now in the Kunsthistorisches Museum in Vienna, Austria.

The church also contains an early 18th-century painting of the Martyrdom of San Cassiano by Antonio Balestra. It depicts the saint being attacked by school children, an act which explains why Saint Cassian of Imola is the patron saint of school teachers.

• Earls, Irene (1987). Renaissance Art: A Topical Dictionary. New York: Greenwood Press. ISBN 0-313-24658-0.
• McGregor, James Harvey (2006). Venice from the Ground Up. Cambridge, Mass.: Belknap Press of Harvard University Press. ISBN 0-674-02333-1.
• Ruskin, John (1976). Whittick, Arnold (ed.). Ruskin's Venice. G. Godwin. ISBN 978-0-7114-4802-5.
• Simonis, Damien (2010). Italy (Country Guide). Lonely Planet. ISBN 1-74179-229-0.
• Walther, Ingo F.; Suckale, Robert (2002). Masterpieces of Western Art: A History of Art in 900 Individual Studies from the Gothic to the Present Day. Vol. 1. Taschen. ISBN 978-3-8228-1825-1.