Amsterdam, capital of the Netherlands, has been called the "Venice of the North" for its more than one hundred kilometres of canals, about 90 islands and 1,500 bridges. The three main canals, Herengracht, Prinsengracht, and Keizersgracht, dug in the 17th century during the Dutch Golden Age, form concentric belts around the city, known as the grachtengordel. Alongside the main canals are 1550 monumental buildings. The 17th-century canal ring area, including the Prinsengracht, Keizersgracht, Herengracht and Jordaan, were placed on the UNESCO World Heritage List in 2010.