In the summer of 1109 the Polish ruler Bolesław III organized an expedition into Pomerania in order to secure his northern boundary. The German king Henry V, incited by Bolesław's half-brother Zbigniew, was about to invade Poland and the Pomeranian raid was a strategic necessity for the upcoming struggle. According to Gallus Anonymus, the purpose of the expedition wasn't just the taking of the castle of Nakło, but forcing the Pomeranians into a decisive battle. Gallus describes the battle in the first chapter of the third book of his chronicle. On 10 August 1109. Bolesław's force, which was besieging Naklo engaged the Pomeranian relief forces and defeated them. As a result the city surrendered to him. Later Bolesław incorporated Pomerania into his realm. In Gallus' chronicle, the defeat of