Matilda's fortunes changed dramatically for the better at the start of 1141. Ranulf of Chester, a powerful northern magnate, had fallen out with the King over the winter and Stephen had placed his castle in Lincoln under siege. In response, Robert of Gloucester and Ranulf advanced on Stephen's position with a larger force, resulting in the Battle of Lincoln on 2 February 1141. The King commanded the centre of his army, with Alan of Brittany on his right and William of Aumale on his left. Robert and Ranulf's forces had a superiority in cavalry and Stephen dismounted many of his own knights to form a solid infantry block. After an initial success in which William's forces destroyed the Angevins' Welsh infantry, the battle went well for Matilda's forces. Robert and Ranulf's cavalry encircled Stephen's centre, and the King found himself surrounded by the Angevin army. After much fighting, Robert's soldiers finally overwhelmed Stephen and he was taken away from the field in custody.