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Alcatraz hidden fortress: Famed federal prison hides 19th century fortress

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Alcatraz has a “hidden fortress,” researchers say. America’s most notorious prison is concealing some hidden history – a 19th century military fortress long forgotten.

According to Fox News on Thursday, Texas A&M researchers using ground-penetrating radar discovered the remains of an old U.S. military fortress – Fort Alcatraz – built during the time of the Civil War. Further research and site testing will now be done to determine if excavation is an option.

Writes Fox News:

“The fort never fired a shot during the war, though it did house Confederate sympathizers jailed for denouncing the federal government. The radar has revealed old fortifications along with buried magazine buildings and tunnels dating from long before the main prison building was erected in 1915.”

More than a million tourists visit the outcrop in the middle of San Francisco Bay each year, walking the hallways where notorious criminals such as George "Machine Gun" Kelly, Mickey Cohen and Al Capone all spent time behind bars.

“I think most people know that in 1848 gold was discovered in California, and before that time San Francisco was really a very small town,” explains Jason Hagin, the historical architect for the National Park Service, which looks after the island.

“But once gold was discovered here, San Francisco became a very important port for the country and for the west coast, and so protecting it really was the point of building the fortress of Alcatraz,” Hagin said. “The fortification is something that is really important to the historical significance of the island itself. In that sense, it is really important to give people a sense of the early part of the island's history.”

Lying beneath the recreation yard and used in the fort’s construction is European cement, possibly the oldest cement mixture found in the U.S.

“Originally, the fortifications were earthen – they are constructed of dirt – but parts of them had concrete over them to reinforce them,” said Dr. Tanya Wattenburg Komas, director of the Concrete Preservation Institute. “The interesting thing is we weren't even making cement in the US at that time,” she explains.

The biggest potential discovery so far is at the south of the prison, underneath Alcatraz’s parade ground.

“This is an area that is of most historical significance to the park service. It is a very important part of the fortifications,” says Texas A&M lead researcher Prof Mark Everett.

“It is called a caponier, and it is a large structure that juts out into the bay and provides defensive cover. We have seen it in the old photographs but it has completely disappeared from present view,” Everett said.

A caponier is a defensive structure which projects into a ditch, or gallery which crosses a section of ditch, to allow gun fire on an assailant.

The research crew picked up a very large signal, suggesting a large proportion of the building may be intact and buried beneath the ground. If correct, archaeologists will soon start excavations, and a new piece of Civil War history will be added to our nation's archives.

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