The Third System of American fortification was the first cohesive network of military protection for the United States. From 1816 to 1867 forts were built to protect New Orleans, Mobile Bay and Pensacola Bay. Since their construction, land subsidence and relative seal level rise have threatened to destroy many of the forts and their subsidiary structures. This thesis examines the threat of sea level rise and land subsidence to the preservation of Third System forts in Louisiana and the Gulf Coast. The analysis of this paper discusses damage already done to forts and subsidiary structures, natural and anthropogenic causes of relative sea level rise, current methods of climate change mitigation, and how environmental conservation is the best path to the structures long-term preservation.