The ancient city of Jerusalem , being on a mountain , was naturally defensible from almost all sides .
City 's major source of fresh water , the Gihon spring , was on the side of the cliff overlooking the Kidron valley .
The ancient city of Jerusalem , being on a mountain , was naturally defensible from almost all sides but its major source of fresh water , the Gihon spring , was on the side of the cliff overlooking the Kidron valley .