Leipzig is, with a population of over 506,000, the largest city in the federal state of Saxony, Germany. It is situated at the confluence of the Rivers Pleiße, White Elster and Parthe. Leipzig is well-known for its university and its trade fair. Germany's first labor party was founded in the city. Leipzig's noteworthy institutions are the opera house and the Leipzig Zoo, which houses the world's largest facilities for primates. The Nikolaikirche (Church of St. Nikolai/Nicholas) was the starting point of peaceful Monday demonstrations for the reunification of Germany. Leipzig's international trade fair in the north of the city is home to the world's largest levitated glass hall. Leipzig is also known for its passageways through houses and buildings. The importance of the Trade Fair and the University in the creation of a vibrant urban life and city politics from the Reformation through the 19th century cannot be overestimated. Leipzig became a center of the German and Saxon liberal movements.