The World's 30 Most Impressive Fortresses

Built by the Hospitaller Order of Saint John of Jerusalem from 1142 to 1271, the Crusader castle in Syria—and a UNESCO World Heritage site—stands as one of the most preserved examples of fortification from the era. Perched on a high ridge, the fortress has both a defensive and attacking mindset that helped keep it safe from would-be pursuers.

On an atoll about 1,000 miles from India, this joint operation between the U.S. and U.K. handles logistical support for troops in the Middle East. The remote location gives it the ability to track satellites and run a Ground-Based Electro-Optical Deep Space Surveillance system. Plus, just managing work on an atoll 34 miles long end to end, but with only 11 square miles provides for an interesting effort.

More known for the equipment that is housed and tested at the site, Edwards Air Force Base debuted America’s first jet, the Bell P-59, in 1942. The first time an aircraft broke the sound barrier was at Edwards. Now home to the Air Force Flight Test Center and NASA’s Dryden Flight Research Center, the base’s sheer size and location to a large salt flat that can naturally extend runways offer help that has lasted throughout decades.

With over 200 buildings and nearly four miles of wall over six different islands, the fortress was originally built in the second half of the 18th century by Sweden on islands at the entrance to Helsinki’s harbor. Having protected Sweden, Russia and now Finland, the fortress uses local rock and a system of bastions over the varied terrain. Serving as a garrison and a harbor, the site was used by the military until 1973. Now it houses private and public apartments and workspaces.

The towering walls of the Fortress of the Orsini further accentuates the fact that the fort uses a cliff as its main protector. Constructed in the 14th Century and renovated a century later, the site has five underground levels to help Italians move through the site undetected and secured. With cisterns to collect rainwater and its own windmill, the fortress withstood multiple attempts on its destruction.

Located on a plateau overlooking the Dead Sea on the edge of the Judean desert, the strategic location created an isolated outpost that Herod the Great built around 31 BC. Constructed as a safe haven in case of revolt, the site also included two palaces. While a fortress for centuries, the last known use of the site was that of a church.

Don’t mind the volcanic hill that houses a castle in western Ukraine. Also known as the Palanok Castle, the site was birthed in the 14th Century and took on many forms over time, including serving as a key prison. With three distinct sections—known as the high, middle and low castle—the 130-plus rooms that once featured over 150 cannons also has a web of underground passages to give it additional intrigue.

Australia and the U.S. combined on Pine Gap’s research facility in the center of Australia, outside of Alice Springs. Opened in 1970, the intensely remote location not only made construction difficult, but allows the facility to monitor the region in near-complete anonymity due to the desolation that surrounds it.

Built under Raven Rock Mountain near the border of Pennsylvania and Maryland, the Cold War gave rise to a site that has been dubbed Site R. Secrecy often clouded the location, meant to facilitate the Continuity of Operations Plan to keep the government moving forward amidst major catastrophe. With that, the secrecy and location give Site R its own aura.

Located within 800 miles of the Arctic Circle, major supplies must get shipped to the U.S.’s northernmost installation during a three-month summer window. While not only hard to get to, the base operates the 12th Space Warning Squadron, an early warning system for Intercontinental Ballistic Missiles. Thule also handles space surveillance.

The legendary geography at the Rock of Gibraltar includes its sheer cliff face, difficult western slope, and location at the southern tip of Europe adjacent to the Strait of Gibraltar. Britain took advantage of this by enhancing medieval structures here, arming and fortifying the top of the rock in the 16th century. Centuries of improvements, including carving tunnels into the rock for armaments, troop movement, and storage, helped Britain to withstand siege attempts. Today the land is still technically a British overseas territory.

Home of NORAD, which monitors pretty much everything in North American airspace, the Cheyenne Mountain Complex uses the mountains around Colorado Springs as fortification. Sitting inside a hollowed-out space in the mountains, the air defense system reached the height of its mystique during the Cold War when it opened in 1967. Its 25-ton blast doors are embedded within the 1,700 feet of granite. After a complete remodel, the buried site reopened for business in 2008.

The largest fort in India covered 700 acres atop a 590-foot-tall hill, complete with towers and walls that have stood since the Maurya Empire built it near the Indian city of Udaipur in the 7th century. Fort Chittorgarh, also dubbed the Fort of Chittor, has a one-mile-long twisty road leading to it with seven gateways guarded by a watch tower and iron-spiked doors. While only 22 of the original 84 bodies of water within the fort still exist, 40 percent of the fort's space was covered by water at one time—enough of a reservoir to hold about one billion gallons of water and, with rainfall, enough to maintain an army of 50,000 for four years without fear of thirst.

The oldest and largest still-inhabited castle in the world, Windsor Castle has been home to British royalty for almost 1,000 years. Now the official residence of Queen Elizabeth II, the castle was built by William the Conqueror in 1070 as a strategic stronghold along the River Thames, guarding the western approach to London high above the river. The stone fortifications were added along the way, allowing the castle, which became a military headquarters building, to withstand multiple battles. Windsor remains a working royal palace, made popular as a royal hunting ground that's close to the capital.

One of America's largest masonry-built buildings was designed in the mid-1800s to ward off pirates from the Gulf of Mexico shipping lanes. Located on Garden Key way out in the Florida Keys, past Key West, Fort Jefferson is made of more than 16 million bricks. It was a massive upgrade from the lighthouse that originally stood on this spot. The fort was in active use through the Civil War, mainly to house prisoners, but its thick walls weren't as impressive by the late 1800s and it was abandoned as a fort. The structure was never fully finished, but the six-sided fort covers 11 of the 16 acres of land on the key and remains a tourist destination.

Built around 880 by Prince Borivoj of the Premyslid Dynasty, Prague Castle stands as the "largest coherent castle complex in the world" at more than 753,000 square feet. Among its structures you'll find palaces and buildings from the Romanesque-style of the 10th century and Gothic architecture from the 14th century. Inside the castle, the St. Vitus Cathedral and St. George's Basilica give this massive fortress extra cultural appeal. Prague Castle has earned its status as an iconic fortress, as wars in the 1600s inflicted major damage upon the structure.

We just couldn't ignore something with "flying fortress" as the nickname, could we? The Boeing-created four-engine heavy bomber debuted with the U.S. Army Air Corp in 1935 as a new plane loaded with machine-gun mounts and bombing capabilities. The B-17 was designed as a low-wing monoplane with aerodynamic features derived from the XB-15, and the amount of guns, bombs, and heft it carried increased with each model. Stories exist from World War II of pilots flying the plane home with up to 600 flak holes.

The Teutonic Order, a Catholic religious group founded as a military order, constructed the world's largest brick castle in Poland on the bank of the river Nogat in 1406. Now designated a UNESCO world heritage site, the fortified monastery, following multiple conservation efforts, stands as the world's largest castle measured by surface area. The Gothic-style brick walls surrounding the castle do little to hide the magnificent visual appeal of the castle's rising interior.

Deployed in 1975, the USS Nimitz—which would become the namesake for an entire class of aircraft carriers—ran 1,092 feet long, with a flight deck of 252 feet. The supercarrier could cruise at more than 30 knots (just over 34 miles per hour). With the ability to hold more than 5,000 servicemembers and 60 aircraft, the nuclear-powered floating fortress soon became the hallmark for the U.S. Navy, with a total of 10 Nimitz-class carriers that are still in service as the Navy's largest vessels.

The U.S. effort to build new military installations after WWI led to the start of Ft. Knox in 1918. Over years, the security and fortification has continued to increase, especially as the fort became home to the United State Bullion Depository, home of the largest portion of the country's official gold reserves. That security starts with an open field and includes layers of granite, concrete, and steel barriers, and that's before you even get to a safe that was built to withstand atomic bombs. Add in the presence of the U.S. Army, digital and visual surveillance, and the potential for every high-tech form of defense imaginable (there are fun rumors of flooding tunnels) and you get America's most secure safe. Of course, nobody really knows how much gold—or valuables of all sorts—is located within the bowels of Fort Knox.