The Dead Sea is the saltiest lake in the world. It is called "dead" because the high salinity prevents any fish or other visible aquatic organism to live in its water. The high density of the water also causes a curious phenomenon: it is impossible for a bather to sink. Its surface is the lowest point on Earth, at an elevation of 417 below sea level. A great place to observe the extend of the Dead Sea is the natural fortress of Masada, reached from the Dead Sea side by a steep trail of 450m elevation. After being the palace of Herod the Great, it was for 967 Jewish Zealots the last stronghold in their revolt against Rome, as it took 15,000 Roman men to build a ramp from the Western side of the plateau to eventually breach their defenses. The siege of Masada has become in Israel a popular story of heroic resolve, with some accounts reporting that the defenders committed mass suicide instead of surrending. Masada is a UNESCO Word Heritage Site.