The Cumans invaded and plundered the eastern part of the kingdom in 1091. The invading Cumans were leading by chieftain Kapolcs, they broke first in Transylvania, then the territory between the Danube and Tisza rivers. The Cumans tried to leave Hungary with their huge booty and prisoners, but King Ladislaus reached and defeated them near the Temes river. Ladislaus offered the Christianity for the Cuman survivors, the majority of them accepted, thus the king settled them in Jászság. The rumor of the losing battle reached the Cuman camp, the Cumans threatened King Ladislaus with revenge and demanded to free the Cuman prisoners. King Ladislaus marched to the Hungarian border to prevent the next invasion. The two armies clashed near Severin, the Hungarian army was victorious, King Ladislaus killed Ákos, the Cuman chieftain. Makk argues that the Byzantines persuaded them to attack Hungary, while the Illuminated Chronicle states that the Cumans were incited by the "Ruthenians". In retaliation, the chronicle continues, Ladislaus invaded the neighboring Rus' principalities, forcing the "Ruthenians" to ask "for mercy" and to promise "that they would be faithful to him in all things". No Rus' chronicle documents Ladislaus's military action.