Łowicz was a residence of Polish primates in the Polish–Lithuanian Commonwealth. They served as regents when the town became a temporary "capital" of Poland during the interregnum. As a result, Łowicz has its own bishop and a basilica in spite of its considerably small size. The ruins of a former bishop's castle can be found on the outskirts of town. Napoleon Bonaparte is believed to have stayed in one of the houses on the main square. Also, the town was at the centre of the largest battle of the German invasion of Poland, the Battle of the Bzura River, in the opening campaign of World War II.