Sea of Galilee
The lake lost importance when the Byzantines lost control of it.  The area came under the control of the Umayyad Caliphate and later Islamic empires.  Except for Tiberias, little by little, the major towns and cities began to be left empty.  In 1187, Saladin defeated the armies of the Crusades at the Battle of Hattin, mainly because he cut the Crusaders off from the valuable fresh water of the Sea of Galilee.