In through the sliding door of the minibus climb four heavy-built Afghans. They take their place on the shuttle bus to the airport next to three Mauritanians, all men.

"I am from Mauritanie," says one of the men to the Afghan behind him, his French burbling with a guttural Arabic accent. "You know Mauritanie?"

"Is African country," says the Afghan, turning away. The minibus pulls round the roundabout outside the city's airport. Flowering plants border a coloured pebble rock-garden, the logo of the Islamic Summit blue and green against a white pebble background.

"Is an Arab country," the Mauritanian says sharply.

The Afghan turns back to him, and says,

"Is an Arab African country." He smiles without friendliness, while the Mauritanian grasps his hand, and laughs.

In Mauritania, a Mauritanian friend told me, not even the Governor of the Central Bank, who is black, would be able to marry the poorest house maid if she was a white Moor. In the Arab world, Mauritanians fight not to be grouped with their black neighbours; no one there wants to be mistaken as African.

On the roundabout, a homeless man, one of Dakar's fantastically-dressed crazy men who wear scraps of cloth and have masses of matted dreadlocks, is intercepted by three gendarmes as he tries to cross the pebbled garden. In this uncharacteristically-sterile environment, created in the flash of Arab funds, his wild staring eyes and bare bony legs look like real life. The rest is just a mirage.