The Sestieri di Citra are: Castello, San Marco, Cannaregio.
Castello: it once was one of the main island on which Venice was built. Its name, meaning Castle, comes from a defensive castle that was built anciently in the area . It is the area where the Biennale takes place.
San Marco (St.Mark): anciently known as Morso (lit.Bite), because its ground was the hardest in town or Brolo (in Venetian small orchard) beause it was full of trees. When the body of St.Mark was brought in the city from Alexandria and the Basilica was established the whole area took the name of St.Mark (from the square surrounding the Basilica).
Cannaregio coming from Canal Regio (Royal Canal) as the Grand Canal in this area is very wide or more probably from the groves of reeds (canneti in Italian) present in the area. It is the area going from Rialto to the Railway Station.
Dorsoduro. It litterally means hardback and it is so called because its soil was hard (duro in Italian) and the island has the shape of a back (dorso in Italian). It is the area of the curch of Santa Maria della Salute and the Accademia Galleries.
S. Polo coming from the church of St.Paul (in Venetian San Polo) built in 837. It is the smallest Sestiere in Venice. It is the Frari area.