After the Mahdi retreated into Kordofan in 1881 he started to raise an army there and in Darfur. A force of 4,000 was sent to capture him, but it was ambushed near El Obeid and destroyed, and all of its equipment captured. The Mahdi's forces had grown spectacularly, and by 1883 British sources placed their size at 200,000, although that is almost certainly an overestimate.