Tunnels, ammunition batteries, buildings found under Alcatraz

A web of tunnels have been found under the grounds of Alcatraz Federal Penitentiary, but they were not used by prisoners who were trying to escape. Rather, experts say the tunnels and other buried structures were built as part of a Civil War-era military fortification.

The findings by archaeologists were recently published in a study "Near Surface Geophysics," where they outlined their hypothesis and what they did to confirm and uncover what they thought to be under the famous prison, The San Francisco Gate reported.

Timothy de Smet, an archaeologist at Binghampton University, said, “These remains are so well preserved, and so close to the surface. They weren’t erased from the island. They’re right beneath your feet.”

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The team of archaeologists used ground-penetrating radar and terrestrial laser scans, instead of shovels and brushes, to uncover what sat below the prison. They also used historical photographs to compare what the high-tech scans found to the historical record, the SF Gate reported.

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They found buildings, underground ammunition magazines and tunnels just below the island prison. Historians think that workers didn’t knock down what was already built on the island, but rather just built over them.

Officially, the land was allocated in 1850 for use as a military reservation by the federal government, according to the history of Alcatraz by the Bureau of Prisons. When planned for a military fortification in the Civil War, using the island's rocky waterfront as a natural defense, brick buildings were put up to hold up to 200 soldiers for up to a four-month siege, the SF Gate reported.

The government made it the most fortified military site on the West Coast, with more than 100 cannons installed on the island, according to the Bureau of Prisons.

In the late 1850s, it was being transformed into a prison and Fort Alcatraz served as the official military prison for the West Coast. It would continue as a prison for more than a century. From 1909 to 1911, military prisoners held on the island built a new prison to replace the army's Citadel that was torn down in 1909. That is the same prison that was first designated as the Pacific Branch, U.S. Disciplinary Barracks for the U.S. Army that is now known as The Rock, the Bureau of Prisons said. In the '30s, the Federal Bureau of Prisons took control with the first federal prisoners coming to the island in the mid-1930s to the prison that was designated as maximum-security, minimum-privilege prison to hold the country's worst inmates. When being held at The Rock, prisoners had only four rights: food, clothing, shelter and medical care. Other privileges had to be earned, like visitation, working and the library. After about five years, and once a prisoner was found to no longer be a threat at a standard prison, they were transferred back to another federal prison.

In 1963, the last prisoner left The Rock, the SF Gate reported.

The history of the island though goes back to 1775, when Spanish explorer Juan Manuel de Ayala sailed into San Francisco Bay and mapped the land in and around the water. He named one of the three islands Alcatraces, which eventually became Anglicized to Alcatraz.

Archaeologists are planning to study the structures that have been hidden for a century to discover what other secrets may be buried below the prison.

Cox Media Group