The Valley of the End is located on the border of the Land of Fire and the Land of Sound. It was formed in the battle between Madara Uchiha, the founder of the Uchiha clan and Hashirama Senju, the shodai Hokage. It was also the location of Naruto's battle against Sasuke Uchiha, when the latter defected from Konoha to join Orochimaru, to gain the power he needed to complete his quest to kill Itachi.
