Protected areas similar to or like Fort Sumter

Series of fortifications on Sullivan's Island, South Carolina, built to protect the city of Charleston, South Carolina. The first fort, formerly named Fort Sullivan, built of palmetto logs, inspired the flag and nickname of South Carolina, as "The Palmetto State". Wikipedia

Decommissioned military installation in Hampton, Virginia, at Old Point Comfort, the southern tip of the Virginia Peninsula, United States. Along with Fort Wool, Fort Monroe originally guarded the navigation channel between the Chesapeake Bay and Hampton Roads—the natural roadstead at the confluence of the Elizabeth, the Nansemond and the James rivers. Wikipedia

List of National Historic Landmarks in South Carolina, United States. Operated under the auspices of the National Park Service, and recognizes buildings, sites, structures, districts, and objects according to a list of criteria of national significance. Wikipedia

Historic artillery battery located at James Island, Charleston, South Carolina. Built in 1863, as part of the James Island Siege Line and protect the Stono River, Johns Island and lower James Island. Wikipedia

Plantation in Dorchester County, directly across the Ashley River from North Charleston and about 15 mi northwest of Charleston, in the U.S. state of South Carolina. The primary residence of several generations of the Middleton family, many of whom played prominent roles in the colonial and antebellum history of South Carolina. Wikipedia

Coastal star fort and the name of a former United States Army post on Governors Island in New York Harbor, within New York City. Oldest existing defensive structure on the island, and was named for John Jay, a member of the Federalist Party, New York governor, Chief Justice of the Supreme Court, Secretary of State, and one of the founding fathers of the United States. Wikipedia