An aerial view of a small village within Fort Bourtange, in the Netherlands, near the German border, seen in autumnal colors. Fort Bourtange was originally completed in 1593, during the Eighty Years' War. Its battlements and moat were restored beginning in the 1960s. #

An overview of Fort McHenry National Monument and Historic Shrine, in Baltimore, Maryland. Originally built in 1798, its bombardment by British forces during the Battle of Baltimore in 1814 inspired Francis Scott Key to write the words to a song that became the U.S. national anthem. #

An aerial view of the city of Halifax and its Citadel National Historic Site, in Nova Scotia, Canada. Photo taken with a drone in September 2023. #

A satellite image of Fort Goryōkaku, in Hakodate, Japan, seen in Google Earth. The fortress was completed by the Tokugawa shogunate in 1866. Today, the site is a city park. #

A tugboat escorts a tanker through Boston Harbor, past Fort Independence on Castle Island, in Boston, Massachusetts, on January 31, 2020. The strategic site, on Boston Harbor, has been the location of a fort since the 1630s. #

The fortified town of Palmanova sits in northeastern Italy. The town was built by the Venetian Republic in 1593. #

Kłodzko Fortress, in the town of Kłodzko, in southwestern Poland. The location has been the site of a series of defensive fortifications for nearly 1,000 years. #

Tilbury Fort, a late 17th-century coastal fort with bastions and outworks, principally Dutch in design. Photographed from above the River Thames, across from Gravesend, England. #

An aerial view of the Citadel of Jaca, seen on a sunny autumn day in northeastern Spain. The fort is now home to the Museum of Military Miniatures. #

Fort Monroe National Monument sits at the entrance to Hampton Roads, in Fort Monroe, Virginia, seen on April 27, 2016. The fort that was deactivated in 2011 was a military installation that guarded the navigational channel in Chesapeake Bay. #

An aerial view of Prince of Wales Fort National Historic Site, across the Churchill River, from Churchill, Manitoba, Canada. The fort was originally a wooden structure built by the Hudson's Bay Company in 1717. #

Kuressaare Castle, in the Estonian town of Kuressaare. The original castle and its fortifications date back to the 14th century. #

An aerial view of the Royal Fortress of the Concepción, situated near the border between Spain and Portugal. The site now houses a hotel. #

An aerial photograph of the Castillo de San Marcos National Monument, in St. Augustine, Florida. The fort was built by the Spanish and first completed in 1695. #

The fortified town of Hulst, Netherlands, seen from above. Its fortifications were first built in the 17th century. #

The Vauban Citadel, Belle-Île-en-Mer, sits across the harbor from Le Palais, in Brittany, northwestern France. #