Grass: A Nation's Battle for Life (1925)

The real-life struggles of the Bakhtiari tribe of Southern Persia (Iran) to migrate with 50,000 people and ten times as much livestock over seemingly impassable natural barriers of mountain and river during harsh weather conditions to reach grazing lands for their cattle and other livestock. Their hardscrabble life is portrayed with poetically beautiful cinematography in possibly the greatest documentary of the silent era.