Its independent existence of the medieval fort was threatened by the continuous Mordvin attacks against it; the major attempt made by forces under Purgaz in April 1229 was repulsed, but after the death of Yuri II on March 4, 1238 at the Battle of the Sit River, the Mongols occupied the fortress. Later a major stronghold for border protection, Nizhny Novgorod fortress took advantage of a natural moat formed by the two rivers.