The Polish–Lithuanian Commonwealth – formally, the Crown of the Kingdom of Poland and the Grand Duchy of Lithuania and, after 1791, the Commonwealth of Poland – was a dual state, a bi-confederation of Poland and Lithuania ruled by a common monarch, who was both King of Poland and Grand Duke of Lithuania. It was one of the larges and most populous countries of 16th– to 17th-century Europe. At its largest territorial extent, in the early 17th century, the Commonwealth covered almost 400,000 square miles (1,000,000 km2) and sustained a multi-ethnic population of 11 million.06
