navigable rivers (Vilnia and Neris), surrounded by impenetrable forests and wetlands. At the time of the 14th century, Lithuania was continuously invaded by the Teutonic Order. The future King of England Henry IV (then Henry Bolingbroke) spent a full year of 1390 supporting the unsuccessful siege of Vilnius by Teutonic Knights with his 300 fellow knights. During this campaign he bought captured Lithuanian women and children and took them back to Königsberg for their conversion to Christianity. King Henry's second expedition to Lithuania in 1392 illustrates the financial benefits of these guest crusaders to the Order. His small army consisted of over 100 men, including longbow archers and six minstrels, at a total cost to the Lancastrian purse of £4,360. Despite the efforts of Bolingbroke and his English crusaders, two years of attacks on Vilnius proved fruitless. Vilnius was the flourishing capital of the Grand Duchy of Lithuania, the residence of the Grand Duke. Gediminas expanded the Grand Duchy through warfare along with strategic alliances and marriages. At its height it covered the territory of modern-day Lithuania, Belarus, Ukraine, Transnistria, and portions of modern-day Poland and Russia. His grandchildren Vytautas the Great and Jogaila, however, fought civil wars. During the Lithuanian Civil War of 1389–1392, Vytautas besieged and razed the city in an attempt to wrest control from Jogaila. The two Gediminids cousins later settled their differences; after a series of treaties culminating in the 1569 Union of Lublin, the Polish–Lithuanian Commonwealth was formed. The Commonwealth's rulers held two titles: Grand Duke of Lithuania and King of Poland. In 1387, Jogaila acting as a Grand Duke of Lithuania and King of Poland, granted Magdeburg rights to the city. The city underwent a period of expansion in the 16th century. The Wall of Vilnius was built for protection between 1503 and 1522, comprising nine city gates and three towers, and in 1547 Sigismund II Augustus moved his court from Kraków to Vilnius. Polish–Lithuanian Commonwealth Vilnius's growth was due in part to the establishment of Alma Academia et Universitas Vilnensis Societatis Iesu by the Polish King and Grand Duke of Lithuania Stephen Báthory in 1579. The university soon developed into one of the most important scientific and cultural centres in the region and the most notable scientific centre of the Commonwealth. During its rapid development, the city was open to migrants from the territories of the Crown of the Kingdom of Poland,