In arid Mauritania, where Sahara desert meets Sahel grasslands, a train stretching up to two and one half kilometers snakes along the northern border. Built to carry iron ore from mines in the northeast to the coastal port city, Nouadhibou, it has developed an equally important second function. It connects far-ranging villages to each other and to the city, where no road has ever been built. Naomi Schwarz has this story from Northern Mauritania.

Wind whistles through the empty landscape. Only a small shack, a road and a train track interrupt the dusty, brown expanse.

A distant rumbling turns into thundering crashes of train cars straining against each other at their joints. The wheels screech on the metal tracks as the train begins to slow.

Hundreds of freight cars pass. The head of the train is long out of sight when the final car appears on the horizon. The train is more than two kilometers long. Once the world's longest train, it has been surpassed by freight trains in Australia that can be twice as long.

But the train seems unaware of its novelty or that the novelty has worn off. It simply continues its business of running, three times a day, between the Atlantic port of Nouadhibou and the mining city of Zouerate, 700 kilometers to the northeast.

On its journey towards the west, the train carries up to 25,000 metric tons of iron ore for export. Heading back east, the freight cars, built like giant, rectangular buckets, are empty, ready to be refilled.

But in both directions the train carries a second cargo. Passengers board the train at both ends of the route and during stops along the way.

Lala Abbas fusses with her cell phone as she waits in the small shack that serves as a train station near Nouadhibou. She is traveling to Zouerate with her two small children to stay with her brother for an upcoming Islamic holiday.

She has paid about $10 for each ticket and will sit in the passenger car attached at the very tail of the train.

But Abbas' father, who is waiting to see his daughter off, says he worked for the mining company since before the train began running until he retired in 2002.

He says the train was not intended for passengers.

But he says, from the start, passengers started boarding the freight train.

It is economic for people, he says, because between Zouaret and Nouadhibou, there is no other way.

There is no road that connects the far away cities or the dispersed villages in between.

When the train began running, passengers began climbing into the freight cars. They perched on top of the iron ore or sat in the empty buckets for the hours-long journey.

Although the mining company eventually added a passenger car, people continue to climb into the freight cars all the same.

Mustafa Taher is a young man from a village near Mauritania's border with Mali. He is traveling east on the train, along with two colleagues from the mining company, and one of the men's sons. They are riding in a freight car near the train's tail.

Taher gestures at the case of tomatoes, sac of potatoes, and giant suitcases the men have hoisted on board. He says they have too much baggage to fit in the passenger car.

Others choose to take the freight cars because they cannot afford the ticket.

The train offers an essential lifeline to the communities along its route, Taher says.

Although seemingly entirely cut off, with no neighboring communities for kilometers in any direction, Taher says they are not isolated, because the train connects them to each other and to the coast.

Even in villages where the train does not stop, people take advantage. Passing through one such village, a young man races alongside, eventually leaping up to climb aboard the still moving train.

Traveling in the iron cars is not luxurious, says Taher, but it is not too bad, especially when you finally arrive.

It is no big deal, he says. When he arrives, he will take a good shower, eat a hot meal, and head to bed.

Taher and his colleagues are clearly veterans of the journey. They quickly change into ratty clothes and cover their suitcases with garbage bags to protect them from the barrage of Saharan sand to come. They wrap turbans around their heads and across their faces, and one, Mohammed Sidi, sports plastic goggles to keep the sand out of his eyes.

And as soon as the train starts moving, they begin brewing Mauritanian tea traditionally served in three rounds. The small kettle boils on a charcoal fire perched on a pile of sand they have spilled in the corner.