First, a bombardment by about 140 Confederate cannons on the Union lines was ordered. The bombardment started about 1 p.m. About 80 Union cannons returned fire. The cannons duel lasted for between one and two hours, depending on the source (most say about an hour). The Confederate artillery chief, General Edward Porter Alexander, had only intended it to last for about 25 minutes. But he then realized it had done little damage to the Union line so he continued. But he also had to worry about running out of ammunition and not have enough to support the charge that was Pickett was about to make. When the Union guns fell silent, Porter thought he had knocked them out. But it was a trick by the Union artillery chief. His guns were waiting for the charge the Union forces knew was coming. Alexander sent word to Pickett he could start his attack.