While Lee remained unaware of Grant's intentions, Union army engineers constructed the longest pontoon bridge of the war. It stretched over deep water, crossing the James from Weyanoke to Windmill Point at Flowerdew Hundred. Work started at 4 p.m. on June 15 and was completed seven hours later. Although most of Grant's infantry crossed the river by boats, the IX Corps, one division of VI Corps, the animals and supply wagons, and a part of the artillery crossed on the bridge on June 15 and 16. By the morning of June 17, more than 100,000 men, 5,000 wagons and ambulances, 56,000 horses and mules, and 2,800 head of cattle had crossed the river without alerting the Confederates. Before the entire army had crossed, Smith's XVIII Corps, followed by Hancock's II Corps, became engaged in the next campaign, Richmond–Petersburg (the Siege of Petersburg), with attacks on Petersburg on June 15.