Every year for over 25 centuries, the 500,000 members of the nomadic Bakhtiari tribes of southern Iran have made a journey of some 200 miles from their winter to their summer pastures.
They take with them several million sheep and other animals, they travel on foot and by mule as they make a journey which can be described as the most hazardous test of human endurance still undertaken year after year by an entire people.
An Anthony David production
Desert interlude: page 5