This, the Blockhouse, is the only thing that remains of the first Fort Trumbull, which was built in 1775. The Blockhouse itself was built in 1794, as part of an effort to upgrade US seacoast defenses that was ordered by president George Washington. While the Blockhouse is alleged to be the only thing still standing from this 1794 period, helloo, might I direct your attention to Fort Norfolk in Virginia.

The Blockhouse was built to house up to 50 troops in wartime, with a magazine for ammunition in the basement. This would have been the fort's citadel, a place to which everyone would scurry should the fort's walls be breached, in the vain hope that holding out just a little longer might somehow turn the tide of the battle.