At the beginning of 1817, the royalist Marshal José de la Serna marched on Salta Province with a large force of experienced soldiers. Güemes organized a popular army and, on 1 March, retook Humahuaca. The royalist army of 5,400 men, with newly arrived reinforcements, was met with a scorched earth retreat combined with continuous guerrilla attacks. De la Serna arrived in Salta City on 16 April, but the population resisted. Faced with lightning skirmishes, declining morale and the news of San Martín's victory in the Battle of Chacabuco, the royalist troops retreated to the north.