This encouraged Stefan Vojislav who continued to expand the state and to provoke Byzantine allies. New emperor Constantine IX Monomachos (ruled 1042-1055) sent a new expedition in the fall of 1042. The army was dispatched immediately after the observation of the comet on 6 October 1042. Numbering 40,000 to 60,000 soldiers, the imperial army was headed by Michael, "dux" of Dyrrhachium. Michael was initially successful. He entered deeply into the Stefan Vojislav's state, amassing lots of "plunder and captives" and decided to return. However, Stefan Vojislav organized an ambush in the ravines of the Rumija mountain. The attack began when the Serbs buried the Byzantines under the massive storm of stones and arrows, throwing them from the mountains above, using all possible sorts of launching weapons. Michael managed to survive, but lost 40,000 soldiers and 7 "strategos". By winning this combat, which became known as the Battle of Bar, Stefan Vojislav suppressed Byzantine rule in this part of the Balkans and solidified his position as the ruler of the unified Serbian state which, for the first time since the migration, encompassed four (out of five) historical principalities: Serbia (Raška, Duklja, Travunia, Zachlumia, and stretched between the rivers of Neretva and Bojana). However, Stefan Vojislav officially kept, albeit merely symbolical, vassal relation to the Byzantine Empire.