The term Serengeti is derived from the Masai language, and means 'Endless Plains'. This area between latitudes 1 and 3 S and longitudes 34 and 36 E hosts the largest and longest overland migration in the world, twice each year. This migration is considered one of the ten natural travel wonders of the world. Around October, nearly 2 million herbivores travel from the northern hills toward the southern plains, crossing the Mara River, in pursuit of the rains. In April, they then return to the north through the west, once again crossing the Mara River. This phenomenon is sometimes called the Circular Migration. Over 250,000 wildebeest alone will die along the journey from Tanzania to Masai Mara Reserve in upper Kenya, a total distance of 500 miles.