Hezekiah's tunnel

Hezekiah's tunnel is a tunnel that was dug underneath Ophel in Jerusalem about 701 BC during the reign of King Hezekiah. The tunnel, leading from the Gihon Spring to the Pool of Siloam, was designed to act as an aqueduct to provide Jerusalem with water during an impending siege by the Assyrians, led by Sennacherib. The curving tunnel is 533m long, and by using a small altitude difference between each end, conveyed water along its length from the spring to the pool.

According to an inscription (the Siloam inscription) found within it, the tunnel was excavated by two teams, one starting at each end of the tunnel and then meeting in the middle. The inscription is partly unreadable at present, and may originally have conveyed more information than this. It is clear from the tunnel itself that several directional errors were made during its construction. Recent discoveries concerning a related tunnel - Warren's shaft - have suggested that the tunnel may have been formed by substantially widening a pre-existing natural karst.

More...