When Hooker received the report about the Confederate movement, he thought that Lee might be starting a retreat, but he also realized that a flanking march might be in progress. He took two actions. First, he sent a message at 9:30 a.m. to the commander of the XI Corps, Maj. Gen. Oliver O. Howard on his right flank: "We have good reason to suppose the enemy is moving to our right. Please advance your pickets for purposes of observation as far as may be safe in order to obtain timely information of their approach."^[9] At 10:50 a.m., Howard replied that he was "taking measures to resist an attack from the west."