Prideaux, advancing up the Mohawk, proceeded to Oswego, where he left half of his men to cover his retreat, and then sailed to Niagara. Slain by accident during the siege, his place was taken by Sir William Johnson, the Indian commander, who pushed the work with vigor. Suddenly confronted by a French force of thirteen hundred rangers and savages from the West, who had been deflected thither from a proposed attack on Pittsburg, with the view of recovering that fort, Johnson completely vanquished them (July 24). The discomfited crew burned their posts in that region and retreated precipitately to Detroit. The following day Niagara surrendered, and thus, with Pittsburg also saved, the West was entirely cut off from Canada, and the upper Ohio Valley was placed in British hands. The work of Stanwix having been accomplished by Johnson, the former, who had been greatly delayed by transport difficulties, advanced as promptly as possible to the Forks of the Ohio, and in the place of the old French works built the modernized stronghold of Fort Pitt.[38] On August 20, Wolfe fell seriously ill. Both he and the army were discouraged. The casualties had thus far been over eight hundred men, and disease had cut a wide swath through the ranks. Desperate, he at last accepted the counsel of his officers, that a landing be attempted above the town, supplies definitively cut off from Montreal, and Montcalm forced to fight or surrender. From September 3 to 12, Wolfe, arisen from his bed but still weak, quietly withdrew his troops from the Montmorenci camp and transported them in vessels which successfully passed through a heavy cannonading from the fort to safe anchorage in the upper basin. Reinforcements marching along the southern bank, from Point Lévis, soon joined their comrades aboard the ships. For several days this portion of the fleet regularly floated up and down the river above Quebec, with the changing tide, thus wearing out Bougainville’s men, who in great perplexity followed the enemy along the cliff-tops, through a beat of several leagues, until from sheer exhaustion they at last became careless. On the evening of September 12, Saunders--whose admirable handling of the fleet deserves equal recognition with the services of Wolfe--commenced a heavy bombardment of the Beauport lines, and feigned a general landing at that place. Montcalm, not knowing that the majority of the British were by this time above the town, and deceived as to his enemy’s real intent, hurried to Beauport the bulk of his troops, save those necessary for Bougainville’s rear guard. Meanwhile, however, Wolfe was preparing for his desperate attempt several miles up the river.