Inside "Hezekiah's tunnel," the 8th century water channel cut through bedrock right under the City of David. The channel brought water from the Gihon spring (on the north-eastern slope of the hill) to the Siloam pool at the southern tip of the city. King Hezekiah ordered construction of this water system to secure a water source inside the city walls in the face of the approaching Assyrian army. When the channel was finished, the entrance to the spring was covered over with rubble to prevent the Assyrians from using (or tampering with) the water.