Here a little geographical explanation is necessary. Petersburg lies on the Appomattox river, twenty-two miles due south of Richmond. It was connected with Richmond by a line of railway and this line was extended from Petersburg southward, by way of Weldon, North Carolina. The Weldon railroad constituted Lee's main line of communication with the coast country south of him. From Petersburg west, extended another line of railway to Lynchburg and beyond, while from Richmond a third line, the Richmond and Danville road, extended southwesterly to Danville, crossing the south side railroad at Burkesville, or as the place was more familiarly known, the Junction. These three lines of railway constituted Lee's sole means of communication with the country south and west of Richmond. It was Grant's purpose, while holding Lee rigidly to his defensive works, to push his own columns around Lee's right and into his rear, threatening and ultimately cutting these three lines of communication. Grant hoped so far to conceal his purposes from his wily adversary as to take Petersburg by surprise and capture it, thus at once and easily breaking two of the three lines of Confederate communication, and gaining possession of a position which McClellan two years before had seen and declared to be the military key to Richmond. In aid of this purpose of surprise he set men at work, throwing up fortifications to the north of Richmond, and sent large bodies of cavalry to operate destructively on the north and west of that city, while he held at and near Cold Harbor a sufficiently threatening line in Lee's front to give the impression that he had determined upon making his siege approach in the same way in which McClellan had sought to take the city two years before. He transferred his base of supplies to the White House on York river, where McClellan's base had been. Then he began his movement upon Petersburg. Sending a large part of his force by water, he moved the rest across the James river by pontoon bridges, all his operations being beyond sight of the Confederates. In his effort to take Petersburg by surprise he was very nearly successful. At the beginning of the movement he had Butler under his command and well placed south of the James river, with an army of 30,000 men. In anticipation of his own movement with the main army, he ordered Butler to advance at once upon Petersburg, capture that place, and hold it until the Army of the Potomac should come up.