Batu Khan, who was the commander of the Mongol armies invading Eastern Europe, demanded Béla IV's surrender without a fight in 1240. The king refused, and ordered his barons to assemble with their retinue in his camp at Pest. Here, a riot broke out against the Cumans and the mob massacred the Cuman leader, Kuthen. The Cumans soon departed and pillaged the central parts of the kingdom. The main Mongol army arrived through the northeastern passes of the Carpathian Mountains in March 1241. Royal troops met the enemy forces at the river Sajó, where the Mongols won a decisive victory in the battle of Mohi on April 11, 1241. From the battlefield, Béla IV fled first to Austria, where Duke Frederick II held him for ransom. Thereafter, the king and his family found refuge in Klis Fortress in Dalmatia. The Mongols first occupied and thoroughly plundered the territories east of the river Danube. They crossed the river when it was frozen in early 1242. A contemporary account by Abbot Hermann of Niederalteich stated that the Kingdom of Hungary, which had existed for 350 years, was destroyed.