Castello is the largest of the six sestieri of Venice. The district grew up from the thirteenth century around a naval dockyard on what was originally the Isole Gemini, although there had been small settlements of the islands of San Pietro di Castello, also called Isola d'Olivolo, since at least the eighth century.

The district became divided between the Arsenale, then the largest naval complex in Europe, and the monasteries in the north of the quarter.

It was later altered by Napoleon, who planned what are now the Bienniale Gardens, and still more recently the island of Sant'Elena has been created, and land drained at other extremities of the quarter.