The Netherlands has 12 provinces: Zeeland, South Holland, North Holland, Friesland, and Groningen, all of which border on the North Sea; and North Brabant, Limburg, Utrecht, Gelderland, Overijssel, Drenthe, and Flevoland. The country is mostly low-lying. About 40% of it is situated below sea level and comprises territory (mostly in the western part of the country) reclaimed from the sea since the 13th cent. and guarded by dunes and dikes. The land is crossed by drainage canals, and the main rivers, the Scheldt, Maas (Fr., Meuse), IJssel, Waal, and Lower Rhine, are canalized and interconnected by artificial waterways, linked with the river and canal systems of Belgium and Germany. The Scheldt estuary includes the former islands of Walcheren, North Beveland, and South Beveland. The West Frisian Islands are located off the northern coast of the Netherlands. The Netherlands is extremely densely populated. The maritime provinces include many of the famous cities of the Netherlands-Amsterdam and Rotterdam (the chief ports) and The Hague, Leiden, Delft, Utrecht, Dordrecht, Schiedam, and Vlissingen (Flushing). In addition, Alkmaar, Gouda, and Edam are internationally known as cheese markets, and Haarlem is the center of the flower-raising district. The inland provinces have generally poor and sandy soil. Leading cities include Breda, 's Hertogenbosch, Eindhoven, and Tilburg in North Brabant; Maastricht and Heerlen in Limburg; and Arnhem and Nijmegen in Gelderland. Linguistic conformity to Dutch, the official language, is complete except in Friesland, where Frisian is spoken in places. After the Netherlands obtained independence in the late 16th cent., it became largely Protestant. By the mid-1990s, however, Roman Catholics, concentrated in the southern provinces, made up the largest religious group (33%), while 25% were Protestant. Muslims are a small but growing minority; almost 40% of the population claims no religious affiliation. The archbishop of Utrecht is the Roman Catholic primate of the Netherlands. The country's principal public universities are at Leiden, Utrecht, Groningen, Rotterdam, and Amsterdam. There are also Catholic universities at Nijmegen and Tilburg and a Calvinist university at Amsterdam. Specialized higher education is offered by Erasmus Univ., technical schools at Delft, Eindhoven, and Enschede, and by the schools of economics at Rotterdam and Tilburg.