The strategic importance of the area limited by the Vistula, Bug, Wkra and Narew was known to various armies throughout the ages. The first fortified stronghold was built in Zakroczym by the Piast dynasty in the 11th century. However, first modern fortified position was built there in 1656 by the Swedish armies during The Deluge. The so-called "Bugskansen" was a star-shaped fortified military camp, located probably close to the confluence of the Narew and the Vistula, at the so-called "Swedish Island". The camp was also guarding a wooden bridge over the Vistula prior to the battle of Zakroczym and served as the main supply depot of the Swedish army during the battle of Warsaw of July 1656. After the Swedish defeat the fort was demolished in 1660 and the area remained unfortified for roughly 150 years.