One end of the canal leads into the lagoon near the Santa Lucia railway station and the other end leads into the basin at San Marco; in between, it makes a large reverse-S shape through the central districts (sestieri) of Venice. It is 3.8 km (2.4 mi) long, and 30 to 90 m (98 to 295 ft) wide, with an average depth of 5 metres (16 feet).
The Grand Canal probably follows the course of an ancient river (possibly a branch of the Brenta) flowing into the lagoon. Adriatic Veneti groups already lived beside the formerly-named “Rio Businiacus” before the Roman age. They lived in stilt houses and relied on fishing and commerce (mainly salt). Under the rule of the Roman empire and later of the Byzantine empire the lagoon became populated and important, and in the early 9th century the doge moved his seat from Malamocco to the safer “Rivoaltus”.