Sir Colin Campbell had effected the relief of the Residency of Lucknow and the withdrawal of its garrison, and he was now free to devote himself to the strategic prosecution of the main campaign. Some delay had to be endured pending the return of the carriage which had conveyed the great convoy from Lucknow to the advanced base at Allahabad; but the interval enabled him to concert the measures necessary for the restoration of British authority in the Gangetic Doab and the opening of communications with Agra and Delhi. Greathed's column on its descent from Delhi had already traversed this region through fire and blood; but the wave of rebellion had closed in upon its rear and obliterated every trace of its hurried progress. Campbell had now not merely to traverse but to subdue and occupy; and this was to be accomplished only by the methodised sweep through the length and breadth of the Doab of columns restoring, as they moved, the British authority, and expelling the numerous bands of mutineers. Sir Colin with a wise perception decided on the fort of Futtehghur as the objective point on which the columns to be employed should converge. For various reasons the possession of this strong place, situated as it was on the Ganges about midway between Allahabad and Delhi, was of great strategical importance. It was close to the town of Furrukhabad, the Nawaub of which was a bitter rebel; and it covered the floating bridge on the Ganges at a point where the states of Oude and Rohilcund met, from which hostile territories the enemy were as yet free to enter the Doab and intercept the communication by the Grand Trunk Road with Agra, Delhi, and the Punjaub. His occupation of Futtehghur, on the other hand, would carry with it the command of the fourth side of the Doab; while Agra, Allahabad, and Delhi, whose respective positions dominated the other three, were already in British possession.