History of Antietam National Cemetery (Bradford - page 36)
approach, we may imagine to-day, though even now can scarcely appreciate the responsibilities of the Union commander, and understand some of the reasons for what, in the nervous anxiety of that moment, might have been considered by some as too tardy a pursuit. He was, however, on the right track ; the van of his army reached Frederick on the 12th of September, Lee, with the greater part of his command, having left it two days before.