Amsterdam’s main canals – the Singel, Prinsengracht, Keizersgracht and Herengracht – form a crescent around the city centre. Although the first canals were built as early as the 14th century, the main network of canals was expanded significantly in the 17th century. In the Golden Age, Amsterdam was almost bursting at the seams, but thanks to the canals, the city could expand into the swampy land around the Amstel River. This massive construction project began in 1613. Fifty years later, Amsterdam had grown to five times its original size. The lots along the Prinsengracht, Keizersgracht and Herengracht were sold to wealthy families and these monumental buildings still attest to the wealth of the Golden Era.