April 11, 1241 - King Bela IV is badly defeated at the Battle of Mohi. Advancing into Hungary after King Bela IV refused to turn over Cuman refugees, the Mongols advanced to Pest where the Hungarian army was gathering. Unwilling to give battle, Bela waited until the Mongols began withdrawing east. Following them, he encamped at the River Sajo after a week of marching. On the evening of April 10, a Hungarian force surprised a Mongol column while it was crossing a key bridge over the river. Defeating it, the Hungarians returned to camp to celebrate. Devising a new attack plan, Batu Khan attacked the bridge in force the next morning and drove off the Hungarian guards by sending a small force across the river to the north. These troops caught the Hungarians in the rear and opened the bridge. Moving across the span, the Mongols soon encountered the main Hungarian army. In a massive pitched battle, the Hungarians inflicted heavy casualties but were compelled to retreat when a second Mongol column, led by Subutai, arrived from the south and attacked their flank. Falling back to their camp, the Hungarians were unable to drive off the Mongols and were ultimately routed. Their defeat opened the country to pillaging and occupation.