Barrancas (Gulf Islands National Seashore, NPS)

Fort Barrancas sits on the bluff where four empires stacked their forts. Spain built San Carlos de Barrancas and the Batería de San Antonio water battery after Gálvez took Pensacola in 1781; the French and British had fortified the bluff before that; and when Florida became American in 1821, the Army Corps of Engineers built the brick fort over the Spanish ruins — six million bricks, walls four feet thick, raised in part by enslaved laborers contracted to the government.

Its one war came early — January 1861, when Florida militia seized the bluff forts and the navy yard while the Federals held Fort Pickens across the bay: the other Sumter standoff, guns facing each other over Pensacola's harbor through the war's first winter. The November 1861 artillery duel between Barrancas and Pickens burned the navy yard and settled nothing; the Confederates abandoned Pensacola in May 1862.

The district keeps all the layers — the American fort, the white-walled Spanish water battery below it, the Advanced Redoubt a thousand yards inland — on the bluff inside the Navy base where three flags' worth of fortifications survived into the National Seashore.

Fort Barrancas is the archive's layered file — the bluff over Pensacola Bay where Spanish, British, and American forts stack on each other, and where the Union-Confederate standoff of 1861 mirrored Sumter across the water.