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In page Nizhny Novgorod:

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The 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. After the death of Yuri II on 4 March 1238 at the Battle of the Sit River, the Mongols occupied the fortress. Later a major stronghold for border protection, the fortress of Nizhny Novgorod took advantage of a natural moat formed by the two rivers.[citation needed]