At a place named Cold Harbor, just six miles outside of Richmond, Virginia and north of the James River, General Grant (USA) decided to end his six week effort to take the Confederate capital by frontal assault. Having lost thousands of men in direct attacks on fortified Confederate positions at Cold Harbor, Grant took a new approach.
After sitting in those lines for several days, General Lee's (CSA) forces awoke one morning to find Grant had pulled his 100,000 man army out of their positions and disappeared. Though not overlooked by Lee, Grant had committed to taking Richmond by cutting off its supply base - Petersburg. By boats and a pontoon bridge the Union troops crossed the James River in force and on June 15, 1864, Grant had his lead men poised to take Petersburg. During this time Lee was still not convinced of Grant's main objective and kept most of his army around Richmond. This left General Beauregard (CSA) with a small force to man the walled defenses around the city, the Dimmock Line, in order to fend off the brunt of the Union offensive.