With more than 100 km of canals, Amsterdam is called the "Venice of the North". The canals divide the city into 90 islands that are linked by more than 1300 bridges. The city has three main canals: Herengracht, Prinsengracht, and Keizersgracht. They were dug in the 17th century and form a semi-circular belt around the city center. Alongside the canals are more than 1500 historic listed buildings.