Napoleon's plan was to attack in strength towards Burgos in between the armies of Blake and Castaños. Once they broke through they were to swing both north and south to envelope the remaining armies. In order to achieve this, Napoleon wanted the exposed Spanish armies to remain in their current advanced positions. To achieve this Marshal Moncey's 3rd Corps opposite General Castaños remained inactive from late October to 21 November while Ney's 4th Corps tried to get to his rear through Burgos and Soria.