See also "invincible" and "unsinkable"

On this day in 1777, one year after the Declaration of Independence, one of my most illustrious ancestors was forced to retreat from Fort Ticonderoga, which at the time was widely considered to be "impregnable" (an adjective later applied to the Maginot Line, with similar results). Despite the quality of the fortifications and the degree to which they had been pumped up in the popular imagination, the general faced a greatly superior force, especially after the British managed to get some cannons up onto one of those large hills which Easterners charitably call "mountains" (a possibility that had apparently eluded or was dismissed by the fort's planners).

Rather than stand his ground and get himself and his men heroically obliterated, General St. Clair exercised the better part of valor and retreated in good order under cover of night. For this he was roundly criticized by the public, who couldn't reconcile the loss with the fort's reputation; a court martial eventually exonerated him, but he never held another field command. As a consolation prize, he got a place on Washington's staff (and was present at Cornwallis' surrender); governorship of the Northwest Territories (which in those days meant the Great Lakes region); and a term as president of the Continental Congress (a position which was superseded by, guess who, Washington).