It is now necessary to look to the enemy. Had the Khalifa allowed the Emir Mahmud to march north immediately after the destruction of the Dervish outpost in Abu Hamed, the course of the operations would have been very different. Mahmud would certainly have defended Berber with his whole army. The advance of the Expeditionary Force must have been delayed until the Desert Railway reached the river, and probably for another year. But, as the last chapter has described, the sudden seizure of Abu Hamed, the defection of the riverain tribes, and the appearance of the gunboats above the Fourth Cataract persuaded Abdullah that the climax of the war approached, and that he was about to be attacked in his capital. He accordingly devoted himself to his preparations for defence, and forbade his lieutenant to advance north of Metemma or attempt any offensive operations. In consequence Berber fell, and its fall convinced the Khalifa that his belief was well founded. He worked with redoubled energy. An elaborate system of forts armed with artillery was constructed outside the great wall of Omdurman along the river-bank. The concentration of Arab and black soldiery from Gedaref, Kordofan, and Darfur continued. Large quantities of grain, of camels and other supplies, were requisitioned from the people of the Ghezira (the country lying between the Blue and White Niles) and stored or stabled in the city. The discontent to which this arbitrary taxation gave rise was cured by a more arbitrary remedy. As many of the doubtful and embittered tribesmen as could be caught were collected in Omdurman, where they were compelled to drill regularly, and found it prudent to protest their loyalty. The strength and tenacity of the ruler were surprisingly displayed. The Khalifa Sherif, who had been suspected of sympathising with the Jaalin, was made a prisoner at large. The direst penalties attended the appearance of sedition. A close cordon around the city, and especially towards the north, prevented much information from reaching the Egyptian troops; and though small revolts broke out in Kordofan in consequence of the withdrawal of Mahmud's army, the Dervish Empire as a whole remained submissive, and the Khalifa was able to muster all its remaining force to meet the expected onslaught of his enemies.