After the destruction of the Mordvin Inäzor Obram, a hillfort named Obran Osh (Ashli) on the site of the future stone Kremlin, in 1221 a small Russian wooden hillfort was founded by Grand Duke Yury II. Located at the confluence of two of the most important rivers in his principality, the Volga (Mordvin "Rav" or "Rava") and the Oka, Obran Osh was renamed Nizhny Novgorod. Its name literally means Lower Newtown to distinguish it from the older Veliky Novgorod. Its independent existence was threatened by the continuous Mordvin attacks against it. The major attempt made by Inäzor Purgaz from Arzamas in January 1229 was repulsed, but after the death of Yury II on March 4, 1238 at the Battle of Sit River the Mongols occupied the fortress and the remnants of small Nizhny Novgorod settlement which surrendered without any resistance in order to preserve what had been developed since Purgaz's attack nine years earlier. Later a major stronghold for border protection, Nizhny Novgorod fortress took advantage of a natural moat formed by the two rivers.