Between 1503 and 1522 the walls were built to protect the city, and at the time it had nine city gates and three towers. Vilnius reached the peak of its development under the reign of Sigismund August, who moved his court there in 1544. In the following centuries, Vilnius became a constantly growing and developing city. This growth was due in part to the establishment of Almae Academia et Universitas Vilnensis Societatis Jesu by the King Stephen Bathory in 1579. The university soon developed into one of the most important scientific and cultural centres of the region and the most notable scientific centre of the Polish-Lithuanian Commonwealth. Political, economic, and social activities were in full swing in the town. In 1769, the Rasos Cemetery, one of the oldest surviving cemeteries in the city, was founded. During its rapid development, the city was open to migrants from both abroad and far reaches of territories of Grand Duchy of Lithuania. Each group made its unique contribution to the life of the city, and crafts, trade and science prospered. During the Russo-Polish War (1654–1667), Vilnius was occupied by Russia for several years. The city was pillaged and burned, and its population was massacred. The city's growth lost its momentum for many years, but the population rebounded, and by the beginning of the 19th century city's population reached 20,000, making the city one of the largest in Northern Europe.