and free Dutch-language courses, which have benefited many immigrants. Cityscape and architecture Amsterdam fans out south from the Amsterdam Centraal station and Damrak, the main street off the station. The oldest area of the town is known as De Wallen (English: "The Quays"). It lies to the east of Damrak and contains the city's famous red-light district. To the south of De Wallen is the old Jewish quarter of Waterlooplein. The medieval and colonial age canals of Amsterdam, known as grachten, embraces the heart of the city where homes have interesting gables. Beyond the Grachtengordel are the former working-class areas of Jordaan and de Pijp. The Museumplein with the city's major museums, the Vondelpark, a 19th-century park named after the Dutch writer Joost van den Vondel, as well as the Plantage neighbourhood, with the zoo, are also located outside the Grachtengordel. Several parts of the city and the surrounding urban area are polders. This can be recognised by the suffix -meer which means lake, as in Aalsmeer, Bijlmermeer, Haarlemmermeer and Watergraafsmeer. Canals The Amsterdam canal system is the result of conscious city planning. In the early 17th century, when immigration was at a peak, a comprehensive plan was developed that was based on four concentric half-circles of canals with their ends emerging at the IJ bay. Known as the Grachtengordel, three of the canals were mostly for residential development: the Herengracht (where "Heren" refers to Heren Regeerders van de stad Amsterdam, ruling lords of Amsterdam, whilst gracht means canal, so that the name can be roughly translated as "Canal of the Lords"), Keizersgracht (Emperor's Canal) and Prinsengracht (Prince's Canal). The fourth and outermost canal is the Singelgracht, which is often not mentioned on maps because it is a collective name for all canals in the outer ring. The Singelgracht should not be confused with the oldest and innermost canal, the Singel. The canals served for defense, water management and transport. The defenses took the form of a moat and earthen dikes, with gates at transit points, but otherwise no masonry superstructures. The original plans have been lost, so historians, such as Ed Taverne, need to speculate on the original intentions: it is thought that the considerations of the layout were purely practical and defensive rather than ornamental. Construction started in 1613 and proceeded from west to east, across the breadth of the layout, like a gigantic windshield wiper as the