It is theorized that at the time of the Great Revolt (2,000 years ago) the Jewish People were digging escape tunnels underneath the Upper City (Jewish Quarter). Here is an example of beginning of one such tunnel. We can never know why the tunnel was not completed.
<a href="//commons.wikimedia.org/w/index.php?title=User:Siebenberghouse&amp;action=edit&amp;redlink=1" class="new" title="User:Siebenberghouse (page does not exist)">Siebenberghouse</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>