The castle was erected between 1346 and 1353 and is made up of one wing to the north-east of the courtyard. It was initially surrounded by a line of fortifications and a ditch which lead to the Łyna River with a bascule bridge. The south-east wing of the castle was built in the 15th century. The 40-meter tower dating back to the 14th century was placed in the eastern corner of the courtyard and reconstructed in the early 16th century, giving the castle a circular look in a square formation. During the reconstruction of the tower, the castle's fortifications were raised to 12 meters in height. This made the castle a major bastion located on the borders of Olsztyn, securing its entrance. The castle belonged to the Bishops of Warmia, which until 1454 was protected by the Teutonic Order. This made the building and Olsztyn a strategic place during the Polish-Teutonic Wars. In 1410, during the Battle of Grunwald, the castle had surrendered itself to the Polish Army without a battle, however, in 1414 the castle was seized after a siegelasting a few days. During the Thirteen Years' War, the castle was being captured multiple times by both powers. The Teutonic Order had endangered the town of Olsztyn once more, and for the last time in 1521. In the years of 1516 to 1521, the administrator of the castle was Nicolaus Copernicus, who protected the castle from a Teutonic siege. In the sixteenth, the castle was also used as the seat for two Warmian Bishops, which at the same time were two writers: Johannes Dantiscus ; and Marcin Kromer who wrote numerous hymns in Latin, as well as scientific documents and literature in Polish. Over time, the castle's militaristic importance diminished and its role for the housing of the Bishops of Warmia became less favourable. In 1758, a direct entrance from Olsztyn was built, and a palace wing was built; the expansion meant that many of the fortifications were deconstructed. In 1779, Prince-BishopIgnacy Krasicki stayed at the castle. After the seeding of Warmia in 1772, the castle was therefore controlled by the state. In 1845, the bridge connecting the castle to the town was replaced with a levee, the ditch was removed. Between 1901 and 1911, the castle underwent various renovations; this included the change in floor levels, and arched windows in the cloister. The castle became the Museum of the Warmian-Masurian Voivodeship in 1946; apart from various exhibitions the museum also hosts the Olsztyn Artistic Summer.
