The surface slope of these hills of Jerusalem is in general inclined downward toward the south-east at an angle of about ten degrees. That angle means that the city drains toward the corner where the deep ravine of the Kidron Valley runs. The Kidron runs all along the eastern side of the city between Jerusalem and the Mount of Olives. It meets the valley of Hinnom, which runs along the south side of the city. The Pool of Siloam (the pool where the blind man washed his eyes) lies in this corner. This pool is fed from the one spring that exists in relation to Jerusalem. The spring is now called The Virgin's Fountain. It is outside the city wall. The Pool of Siloam was inside the ancient city wall. Hezekiah, as the result of a dream connected the spring and the pool by a tortuous tunnel right through the rocky hill. The chisel-marks show that the workmen had started from each end, meeting at last in the middle.

How they conceivably could do so without heavy equipment in a tunnel cut through limestone that takes four or five decisive curves in its course, still baffles the archaeological imagination. The tunnel was cut in this way because an enemy was threatening the city, and the king wanted a fresh water-supply within the walls. The porous nature of the limestone is said to be responsible for the intermittent character of the spring. The water percolates gradually into a hidden natural cistern until it reaches an exit at the top. Having filled that exit it siphons out in a swift stream, and then no more water flows until the hidden and never yet discovered cistern is re-filled. The peasants of Jesus' day, as at the present time, believed that it flowed when an angel disturbed the waters.