Researchers find a network of tunnels under the Alcatraz prison

A network of tunnels has been located under the prison cells of Alcatraz.

Texas A&M University found the numerous tunnels, now no longer usable, during research at the former island jail. Yahoo reports that the tunnels were from a time before the prison was in use for military purposes.

Researchers believe that the tunnels were specifically used to move men and ammunition. While they could not physically reach the tunnels, penetrating radar technology was able to local the fortress, according to Fox News. The radar uses a transmitter and a receiver to send waves into the ground allowing the structures underneath the prison to be reflected back.

The main prison of Alcatraz was constructed after the use of this fortress in 1915. The prison was famously known as “escape proof”, BBC reports. Now, the prison is a well-known tourist attraction, receiving about a million tourists every year.

It is also reported that archaeologists plan to excavate the area soon to further research what’s down there.