Battle of 1047 between Casimir I and Miecław

The Battle of Casimir I with Miecław was fought in 1047, during the Miecław's Rebellion, between the Duchy of Poland led by Casimir I the Restorer and its ally, Kievan Rus' led by Yaroslav the Wise, against the forces of Miecław, the self-proclaimed leader of his state, with his ally, the Duchy of Pomerelia. The battle was fought near an unknown river in Masovia.

It was part of a campaign organized by Casimir I, during which, he had invaded Miecław's state. The battle ended with a decisive Polish victory, the death of Miecław, and the destruction of his forces. Subsequently, Miecław's state was reincorporated into Poland soon after.

Background
Following the death of Mieszko II Lambert, king of Poland, in 1034, and the exile of his son, Casimir I the Restorer, to Kingdom of Hungary, the Duchy of Poland had fallen into a period of destabilization, that led to the start of the 1038 Peasant Uprising. Seizing the opportunity, around 1038, the cup-bearer Miecław had formed the state in Masovia, declaring its independence from Poland, and started his own royal dynasty.

Casimir I the Restorer, duke of Poland, had returned to the country from his exile in 1039. He had formed an alliance with Yaroslav the Wise, Grand Prince of Kiev, the leader of Kievan Rus', via the marriage of Maria Dobroniega with Casimir. Expecting the attack from Rus', Miecław had formed an alliance with the Duchy of Pomerelia and Yotvingians. In the spring of 1041, he had begun the campaign against Polish forces. Miecław's forces had fought with the army led by Casimir and Yaroslav, in the Battle of Pobiedziska. The battle ended with a decisive Polish victory and destruction of Miecław's army and led to the signing of the truce between both sides.

The battle
The fighting had begun again in 1047, as Casimir I, together with Yaroslav, had organized the attack on Masovia, which lead to the battle of their forces against the forces of Miecław and Pomerelia. The location of the battle remains unknown in modern times, though it was known to the 11th-century historian, Gallus Anonymus, according to whom, it took place near the river, with the bluff edge. The battle was probably initiated by Casimir I, who hoped to win before the arrival of the Pomerelian army. The battle itself was fierce, with numerous casualties on Miecław's side. The battle ended with Polish victory, following which, Miecław's state was reincorporated into Poland.

Casimir had almost died in the battle but was saved by a soldier, who later had been rewarded for his actions. According to Gallus Anonymus, Miecław had died in the battle. However, according to Wincenty Kadłubek in his Chronica seu originale regum et principum Poloniae, he had escaped to Prussia, where he was murdered.

Army sizes
According to Gallus Anonymus, Miecław's forces had 30 divisions of cavalry, while Casimir, 3 divisions. It is probable that he did not account for the forces of Yaroslav the Wise, and that both sides, in fact, had a similar number of forces.