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With the help of ground-penetrating radar and sending electromagnetic waves into the 150-year-old tunnel, researchers from Texas A&M University came across different structures that lay underneath the Alcatraz prison. They have been able to map out the secrets of 19th century tunnels hidden underneath the old prison’s yard.
Also, they have leaked some of the defense systems which were used by at that time. From 1850 to 1907, many American notorious criminals were locked at Alcatraz prison, said Mark Everett, an A&M professor of geology and geophysics. Alcatraz Island served as a military base for West Coast Confederate sympathizers during the American Civil War.
On analyzing the tunnel systems, researchers found that the defense structures, built in mid-1850s, included barracks and gun batteries. The most surprising fact is that some of the tunnels were reinforced with concrete and were built mostly from earth, the time when cement was not used in the US.
Tanya Wattenburg Komas, from California State University Chico and director of the Concrete Preservation Institute, predicted that the cement might have been carried away in barrels from Europe.
Jason Hagin, an architect for the National Park Service, said that the presence of these defense structures could prove historically valuable. Researchers believe that there exist 12 feet or bigger structures of original fortifications under the surface.