The value of the information that could be obtained, both passively and actively, by black Americans behind Confederate lines was clearly understood by most Union generals from early in the war. A stream of articles and stories in the Northern press during the war highlighted the important role of southern African Americans. Gen. Robert E. Lee, commander of the Confederate Army of Northern Virginia, was equally aware, and in May 1863 he said, "The chief source of information to the enemy is through our Negroes." Because of the culture of slavery in the South, Negroes involved in menial activities could move about without suspicion. Also, officials and officers tended to ignore their presence as personal servants when discussing war-related matters. Confederate General Patrick Cleburne explained the problem in a letter to Confederate high command, complaining "All along the lines slavery is comparatively valueless to us for labor, but of great and increasing worth to the enemy for information. It is an omnipresent spy system, pointing out our valuable men to the enemy, revealing our positions, purposes, and resources, and yet acting so safely and secretly that there is no means to guard against it. Even in the heart of our country, where our hold upon this secret espionage is firmest, it waits but the opening fire of the enemy's battle line to wake it, like a torpid serpent, into venomous activity."