In the centre of Krakow is the Rynek, the main square, which is lined with exquisite medieval buildings. The Cloth Hall is in the centre of the Rynek and has been used for textile trading since the 16th century. Overlooking the square is St. Mary’s church. Nearby is the University and Collegium, where Copernicus theorised that the Earth was not the centre of the Solar System, and the famous Oskar Schindler factory. Dominating Krakow is Wawel castle which dates to the 11th century and is built on a bend on the River Vistula.