Looking across the interior of Fort Griswold from just inside the main gate. Yep, that's the whole thing!

As the excellent diorama of the Battle of Groton Heights in the nearby Monument House Museum (which was not open when I visited, so I haven't seen this diorama in person, but one assumes that the pictures one finds on the internet are reasonably representative) shows, there was a while lot more to Fort Griswold in 1781 than there is today. This included interior buildings (one long, red-roofed barracks ran along the south wall, which we are facing in this image), an unbroken series of pointy logs poking out from the fort's walls in a menacing fashion, and, of course, around 120 armed and stalwart Americans.