It’s a bit of a surprise to walk in and see how pretty this church is, since the outside is a rather nondescript mustard-brown box. Founded in the 8th century or so, this church has been rebuilt and remodeled as many as six times, and the building we see today dates to 1611. The campanile is much older, 13th century with parts dating back to the 9th century; some think it was originally a defensive tower rather than a bell tower.
This church is on the border between San Polo and Santa Croce, and is not to be confused with the church of San Canciano on the other side of the Grand Canal in Cannaregio. Different church and different saint. This one is dedicated to 4th century martyr, St. Cassian of Imola. He's the patron saint of school teachers despite the fact that he died at the hands of his pagan students who stabbed him to death with their ink pens (there’s a Baroque painting of this gruesome/funny scene in the church). San Cassiano’s body is here along with other relics that include the head of St. Cecilia and the jawbone of St. Lawrence Martyr.
John Ruskin said that the only thing worth seeing of the building itself is a Byzantine door fragment leftover from an earlier incarnation, but proclaimed that San Cassiano is a “don’t miss” because of its paintings by Tintoretto. Many of the churches of Venice have at least one painting by Tintoretto, but this church has three, all on the high altar (The Crucifixion, The Descent into Limbo, and The Resurrection). Ruskin declared this Crucifixion as “among the finest in Europe.” Writer Henry James was gaga over this painting too.
This church is also known for its lost altarpiece by Sicilian painter Antonello da Messina, who is believed to have introduced oil painting to northern Italy; he spent a couple of years in Venice studying with (or teaching) Giovanni Bellini. The Pala di San Cassiano disappeared mysteriously from the church in the early 17th century. It was divided into smaller paintings which were dispersed, but three of the pieces have been reunited and are now in the art museum in Vienna. You can see a diagram here that shows how much of the altarpiece was recovered (most of it is still missing). It gives me chills to think about cutting up a painting like this! I wonder if the church needed money to rebuild for the umpteenth time and sold it?