Diallo Munnyal has become rich by playing the cattle markets of West Africa: buying cows in Boni (in southern Mali) and selling them in Djibo, or buying in Djibo and selling in Ouagadougou, in the centre of Burkina Faso. His one problem is transport. He has the option of transporting the cows by lorry, at 5,000 CFA (£5) per head, but why should he do that when he can pay a few soggoobe a pittance to walk the whole herd there?

All over Africa, nomadic ways of life are fast disappearing, and the Fulani people of West Africa are no exception. Yet not all Fulanis have chosen Munnyal’s mercantile lifestyle — some men still lead their lives on the move, walking through the bush behind a herd of cows. These are the soggoobe, professional cattle-drivers who are paid to take other people’s animals to distant markets. Enduring scorching days and sleepless nights, they claim they have the hardest job on earth.

Every Thursday morning a group of soggoobe leaves Djibo and begins the long walk to Ouagadougou, a journey of nine days. I wanted to tag along.

Dikko Idrissa is from Jaw-jaw, a small village near Djibo. He is 47, and has been doing soggal since he was a boy. Starting today, he is responsible for a herd of 96 cows that Mr Munnyal wants to sell in Ouagadougou. From a group of clamouring herders (“Choose me! Choose me!”), Idrissa has picked three men to walk with him: Boureima (his nephew); Macha, from Monde So; and Diallo Hama, a young man from Mali. At the last minute, there was some commotion when a tuubaaku (white man) asked to accompany them; the matter was referred to Munnyal, who laughingly agreed.

“I will not pay you,” Munnyal said to me, chuckling. “But I do not own the road. Go if you want to.”

The cows moved off, with the four herders clicking and whooping behind them. Munnyal handed me a staff and said: “Allah moyyin’ laawol.” (“May God prepare your way.”) Someone else murmured: “O halkan de.” (“He will be destroyed.”) The grim prediction rings in my ears as I trot off to join the soggoobe.

IT IS 11 o’clock, and Djibo town is out of sight. There is only sand and thorn trees, stretching on every side to a flat horizon.

“Soggal hurts,” says Idrissa tonelessly.

“Where?” I ask.

“Legs.”

Boureima is on the west side of the herd, and he cries out: “Lower back!”

“The sun hammers your head,” calls Diallo Hama cheerfully.

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