Tienen or Thienen (both: tēˈnən) [key], Fr. Tirlemont, commune (1991 est. pop. 31,567), Flemish Brabant prov., central Belgium. It is a commercial and industrial center, with a major beet-sugar refining industry. Tienen has suffered numerous sieges in its history. In 1831 the last fighting in the struggle for Belgian independence occurred there. Of note is the Church of Notre Dame du Lac (1296).