	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 largest and most populous countries of 16th- to 17th-century Europe. At its largest territorial extent, in the early 17th century, the Commonwealth covered almost and sustained a multi-ethnic population of 11 million. Polish and Latin were the two co-official languages. 