Jefferson, in his Notes on Virginia, says is worth a voyage across the Atlantic to see.
On September 15, while encamped in the vicinity of Darnestown, we were ordered, late in the day, to break camp and take the road toward the west. Our destination was not disclosed to us, and there was a great deal of speculation among the men as to the object of this secret and hurried march. The next day we found out from citizens along the road that we were on the way to Frederick City, the capital of Maryland. We arrived there late on the afternoon of the 16th, and received an enthusiastic welcome from the citizens of that loyal town. Early the next morning, guards were stationed on all roads leading out of town, and detachments of men, accompanied by detectives, proceeded to arrest the members of the Maryland Legislature, who had assembled there for the purpose of passing an ordinance of secession. It was thus that Maryland was saved to the Union by the promptness of General McClellan. Her secessionist legislators found themselves, shortly after, assembled at Fort McHenry, with leisure to meditate upon their schemes.