At the start of 1849, Amir Dost Mohammed Khan of Afghanistan sided with the rebellious Sikhs, who agreed to cede the city of Peshawar and its surrounding area which had been conquered by Ranjit Singh early in the nineteenth century. Dost Mohammed Khan's support of the Sikhs was cautious, but when 3,500 Afghan horsemen approached the vital fort of Attock on the Indus River, its garrison of Muslim troops installed earlier by Nicholson defected. This allowed Chattar Singh to move out of Hazara and march west and then south, intending to link up with Sher Singh's army. Dalhousie had earlier ordered Gough to halt operations while waiting for Multan to fall, which would allow Whish to reinforce him. Learning of the fall of Attock, he instead ordered Gough to destroy Sher Singh's army before Chattar Singh could join him.