One of the hallmarks of life in Amsterdam is its system of canals, which span more than 60 miles and are traversed by some 1,500 bridges. They have their roots in the Singel Canal, which served a function as a moat around the city from Medieval times until the late 16th century when the city spilled over its banks.
In the early 17th century, with immigration an issue, the principal canals Keizersgracht, Herengracht, and Prinsengracht were constructed to form a belt around the city. The canals effectively centralized life and provided more order to the teeming residential areas of the port city. An outer canal, presently known as Nassau/Stadhouderskade, was also constructed during this time to enable defense and management of the waterways.