Third system forts were constructed between 1817 and 1867. These elaborate enclosed masonry structures were equipped with many smoothbore iron cannons.
During this era, the largest smoothbore canons could fire up to 3 miles. This advance in distance from the second system allowed the Narrows to be the primary defense location of the southern approach to New York Harbor. Fort Richmond, Fort Tompkins, Fort Hamilton, Fort Lafayette, and the Fort at Sandy Hook (never completed) were constructed to guard the southern entrance into New York.
These fortifications were used during the Civil War. An example of a potential enemy was the CSS Virginia, a steam-propelled ironclad ship, like many constructed during the Civil War by both the Confederacy and Union.
Learn more about third system fortifications in today's Fort Wadsworth.
Learn more about the third system, Fort at Sandy Hook
Learn more about the next generation of fortifications, the Endicott Era Defenses.