In 926 a battle was fought in the Bosnian highlands between the armies the Bulgarian Empire, under the rule of Bulgarian Tsar Simeon I, who at the time also fought a war with the Byzantine Empire, and the Kingdom of Croatia under Tomislav, the first king of the Croatian state. The battle is also known as the Battle of the Bosnian Highlands (Bulgarian: Битка при Босненските планини, Croatian: Bitka na Bosanskim visoravnima). It was fought in the mountainous area of Eastern Bosnia near the rivers Bosna and Drina, the border area between the Kingdom of Croatia and the Bulgarian Empire.