One of the events that greatly contributed to the city's development was the Polish-Lithuanian Union of Krewo in 1385. Lublin thrived as a centre of trade and commerce due to its strategic location on the route between Vilnius and Kraków; the inhabitants had the privilege of free trade in the Grand Duchy of Lithuania. The Lublin Parliament session of 1569 led to the creation of a real union between the Crown of the Kingdom of Poland and the Grand Duchy of Lithuania, thus creating the Polish–Lithuanian Commonwealth. Lublin witnessed the early stages of Reformation in the 16th century. A Calvinist congregation was founded and groups of radical Arians appeared in the city, making it an important global centre of Arianism.