By Keith Griffith For Dailymail.com
Published: 19:33 GMT, 1 March 2019 | Updated: 19:33 GMT, 1 March 2019
High-tech laser and radar scans have uncovered a buried military traverse underneath Alcatraz penitentiary.
Archaeologist Timothy de Smet of Binghamton University used advanced scanning technology to discover the buried earthworks on the San Francisco island, publishing his findings in January.
Though Alcatraz is well-known as the former federal prison that housed notorious killers and gangsters, but before that it was a U.S. military installation.
President Millard Fillmore first designated the island for military use in 1850, and the installation became a fort and later a military prison that held POWs in the Civil War.
Archaeologist Timothy de Smet of Binghamton University uses advanced scanning technology to discover the buried earthworks on the San Francisco island
A sketch of Alcatraz Island shows its early days as a U.S. military installation
After the island was transferred to the Bureau of Prisons in 1933, little was thought to remain of the original military fortifications.
But using his scanning technology, de Smet discovered the remnants of underground structures, including a 'bombproof' earthwork traverse