AMERICAN COASTAL DEFENSE THIRD SYSTEM FORTS: HOW GEOMORPHOLOGY DICTATED PLACEMENT AND INFLUENCED HISTORY

After the War of 1812, it was very apparent that the United States needed a stronger, more uniform coastal defensive system. With the notable exception of Fort McHenry, many of the earlier coastal forts proved ineffective against the British forces. A total of forty-two Third System coastal defense forts were built from 1816-1867, many of which continued in use through World War II. Because of their purpose, the locations for Third System forts were limited to islands, shoals, shorelines, riverbanks, or hilltops. The majority of these forts are along the Atlantic and Gulf of Mexico shorelines, extending from Maine to Louisiana. Many of these forts are situated upon a variety of distinctive geomorphic landforms, related to coastal features influenced by Pleistocene sea level changes.

A selection of southeastern Atlantic and Gulf Coast forts will be discussed here that illustrate particular geologic and geomorphic aspects. Fort Pulaski (Cockspur Island), that protected Savannah Harbor, was built on an alluvial island, while Fort Clinch on Amelia Island, that guarded the mouth of the St. Mary’s River, is located on a Holocene barrier island. Of the forts that surround Pensacola Bay in Florida, Forts Pickens (Santa Rosa Island) and McRee (Perdido Key) were also built on Holocene barrier islands, while Fort Barrancas is on the high ground of the Late Pleistocene Pamlico marine terrace.

The history, use, and subsequent threats to these Third System forts can be directly related to the geomorphic systems in which they were constructed. Although militarily outdated, they still represent a remarkable aspect of the military history of the United States.