After the Battle of Tudela two corps had been available to attack Saragossa - the 3rd corps under Marshal Moncey and the 6th Corps under Marshal Ney. Both of these corps left Tudela on 28 November and arrived at Saragossa on 30 November. They were about to commence the siege when Marshall Ney was ordered to take his army across the mountains to New Castille where he was to prevent the army of Castaños, retreating from Tudela, from interfering with his movements towards Madrid.