The more than hunred kilometer of canals in Amsterdam, about 90 islands and 1500 bridges have led the city to being termed the "Venice of the North". The three main canals Herengracht, Prinsengracht, and Keizersgracht, dug in the 17th century, during the Dutch Golden Age, form a concentric belt around the city, known as the grachtengordel. Alongside the main canals are 1550 monumental buildings.