The Hollandse Waterlinie (Dutch Water Defence Line) dates back centuries and was mainly a military border of defensive works from the Zuiderzee (now IJsselmeer) till the Biesbosch (east of Rotterdam). The purpose was to flood areas where the armies of the enemy were approaching from. The Dutch Water Defence Line (and its later successor) has, however, never served its original purpose, although it was partially used three times. The first time was in 1870 when the French-German war threatened to become a European war. The second time was during the Great War and the last time was in 1939 when World War II erupted. Today, there is plenty to do along the 85km defensive works, as each fort now has a different function. They now serve as wine cellars, scouts' centres, conference centres and training facilities for police dogs. Others have become ruins.