ENThis paper analyzes the construction, features, and significance of the Marienwerder castle, and its capture by Lithuanian forces in 1384. Located in what is now Kaunas, the castle represented the furthest eastern point of the Teutonic Order’s penetration into the Grand Duchy of Lithuania. As the sparse historiography on it suggests, the event seems to have been overlooked by contemporary historians. In fact, this castle of the Teutonic Order was not just an ordinary fortress, but a mighty stronghold. A detailed analysis of primary sources allows classifying the capture of Marienwerder as a major event in the war between the Order and the Grand Duchy of Lithuania as well as one of the major victories scored by the latter. It may be concluded that the Teutonic Order’s expansion to the east, which had been started from Torun, was then stopped at Kaunas. [From the publication]