You may think you're looking at a picture of the Groton Monument, but in point of fact, you are not. You're looking at a picture of Fort Griswold's Ravelin! A Ravelin was generally a triangular, free-standing bastion built in front of a fort's main gate to protect it from direct artillery fire.

In the map of Fort Griswold and its environs that you've already carefully studied earlier in this collection, you saw that the Ravelin of our Current Interest looks kind of like a pointy eyebrow from above, but from down here it looks like...another undistinguished mound. I spent a few minutes being puzzled by this mound, which had obviously been placed in this position for some purpose, but...but. Even as non-obstructive as it looks now, it would have served its purpose of deflecting cannon fire away from the main gate, as there was no higher ground nearby where an attacker might place artillery.