One thousand years later, in the eighth century B.C., King Hezekiah of Judah constructed a tunnel that diverted the waters from the spring to a pool on the western side of the city—probably to safeguard the water supply in the event of an Assyrian siege. The beginning of his 1,750-foot tunnel appears in blue in the plan. Around the same time, a second city wall was built outside the spring, in line with the Spring Tower.