 In the seven weeks that followed the occupation of Arlington and the beginning of work on Fort Corcoran, Barnard and his engineers were forced to focus virtually all of their effort on Corcoran and Runyon, owing to the limited resources available.By the time Barnard was beginning to focus his efforts on tying Corcoran and Runyon into an entire belt of fortifications, his engineers were drawn off by the approach of the Confederate Army and the incipient First Battle of Bull Run.Following the Union defeat at Bull Run, panicked efforts were made to strengthen the forts built by Barnard in order to defend Washington from what was perceived as an imminent Confederate attack.