Gdańsk (Polish pronunciation, English:) is a Polish city on the Baltic coast. It is the capital of the Pomeranian Voivodeship, Poland's principal seaport and is also the centre of the country's fourth-largest metropolitan area. The city lies on the southern edge of Gdańsk Bay (of the Baltic Sea), in a conurbation with the city of Gdynia, spa town of Sopot, and suburban communities, which together form a metropolitan area called the Tricity (Trójmiasto), with a population approaching 1.4 million. Gdańsk itself has a population of 460,427 (December 2012), making it the largest city in the Pomerania region of Northern Poland. Gdańsk is the capital of Gdańsk Pomerania and the largest city of Kashubia. With its origins as a Polish stronghold erected in the 980s by Mieszko I of Poland, the city's history is complex, with periods of Polish rule, periods of Prussian or German rule, and periods of autonomy or self-rule as a "free city". Between the world wars, the Free City of Danzig was in a customs union with Poland and was located between German East Prussia and the so-called Polish Corridor. Gdańsk lies at the mouth of the Motława River, connected to the Leniwka, a branch in the delta of the nearby Vistula River, which drains 60 percent of Poland and connects Gdańsk with the Polish capital, Warsaw. Together with the nearby port of Gdynia, Gdańsk is also an important industrial center. In the late Middle Ages it was an important seaport and shipbuilding town, and in the 14th and 15th centuries a member of the Hanseatic League. In the interwar period, owing to its multi ethnic make-up and history, Danzig lay in a disputed region between Poland and the Weimar Republic, and later Nazi Germany. The city's ambiguous political status was exploited, furthering tension between the two countries, which would ultimately culminate in the Invasion of Poland and the first clash of the Second World War just outside the city limits. In the 1980s it would become the birthplace of the Solidarity movement, which played a major role in bringing an end to Communist rule in Poland and helped precipitate the collapse of the Eastern Bloc, the fall of the Berlin Wall and the dissolution of the Soviet Union. Gdańsk is home to the University of Gdańsk, Gdańsk University of Technology, the National Museum, the Gdańsk Shakespeare Theatre, the Museum of the Second World War, Polish Baltic Philharmonic and the European Solidarity Centre. The city also hosts St. Dominic's Fair, which dates back to 1260, and is regarded as one of the biggest trade and cultural events in Europe.