The city is cut by about 40 concentric and radial canals that are flanked by streets and crossed by 400 bridges. The canals give the city its nickname, "Venice of the North." Because of the underlying soft ground, Amsterdam is built on wooden and concrete piles. The many old and picturesque houses along the canals, once patrician dwellings, are now mostly offices and warehouses. The main streets of Amsterdam are the Dam, on which stand the Nieuwe Kerk (15th–17th cent.) and the 17th-century Dam Palace (formerly the city hall, since 1808 a royal palace); the Damrak, with the stock exchange (completed 1903); and the Kalverstraat and Leidenschestraat, which are the chief shopping centers. Notable buildings are the Oude Kerk [old church], built in 1334; the weighhouse (15th cent.); the city hall (16th cent.); and the Beguinage (Dutch Begijnenhof ), or almshouses, of the 17th cent. An ethnically diverse city, Amsterdam has many new residents from former Dutch colonies, including Indonesia and Suriname. Near Amsterdam is the Bosplan, an enormous man-made national park.