THE MEGACITY.

The Third Mainland Bridge is a looping ribbon of concrete that connects Lagos Island to the continent of Africa. It was built in the nineteen-seventies, part of a vast network of bridges, cloverleafs, and expressways intended to transform the districts and islands of this Nigerian city--then comprising three million people--into an efficient modern metropolis. As the bridge snakes over sunken piers just above the waters of Lagos Lagoon, it passes a floating slum: thousands of wooden houses, perched on stilts a few feet above their own bobbing refuse, with rust-colored iron roofs wreathed in the haze from thousands of cooking fires. Fishermen and market women paddle dugout canoes on water as black and viscous as an oil slick. The bridge then passes the sawmill district, where rain-forest logs--sent across from the far shore, thirty miles to the east--form a floating mass by the piers. Smoldering hills of sawdust landfill send white smoke across the bridge, which mixes with diesel exhaust from the traffic. Beyond the sawmills, the old waterfront markets, the fishermen's shanties, the blackened facades of high-rise housing projects, and the half-abandoned skyscrapers of downtown Lagos Island loom under a low, dirty sky. Around the city, garbage dumps steam with the combustion of natural gases, and auto yards glow with fires from fuel spills. All of Lagos seems to be burning.

The bridge descends into Lagos Island and a pandemonium of venders' stalls crammed with spare parts, locks, hard hats, chains, screws, charcoal, detergent, and DVDs. On a recent afternoon, car horns, shouting voices, and radio music mingled with the snarling engines of motorcycle taxis stalled in traffic and the roar of an air compressor in an oily tire-repair yard. Two months earlier, a huge cast-iron water main suspended beneath the bridge had broken free of its rusted clip, crushing a vacant scrap market below and cutting off clean water from tens of thousands of the fifteen million people who now live in Lagos.

In the absence of piped water, wealthier residents of the waterfront slum at the end of the bridge, called Isale Eko, pay private contractors to sink boreholes sixty feet deep. All day and night, residents line up at the boreholes to pay five cents and fill their plastic buckets with contaminated water, which some of them drink anyway. Isale Eko is the oldest and densest part of Lagos Island. Every square foot is claimed by someone--for selling, for washing, even for sleeping--and there is almost no privacy. Many residents sleep outdoors. A young man sitting in an alley pointed to some concrete ledges three feet above a gutter. "These are beds," he said.

In the newer slums on the mainland, such as Mushin, rectangular concrete-block houses squeeze seven or eight people into a single, mosquito-infested room--in bunks or on the floor--along a narrow corridor of opposing chambers. This arrangement is known as "face me I face you." One compound can contain eighty people. In Mushin, Muslim Hausas from the north of Nigeria coexist uneasily with mostly Christian Yorubas from the south. Armed gangs represent the interests of both groups. On the night of Febru-ary 2, 2002, a witness told me, a Hausa youth saw a Yoruba youth squatting over a gutter on the street and demanded, "Why are you shitting there?" In a city where only 0.4 per cent of the inhabitants have a toilet connected to a sewer system, it was more of a provocation than a serious question. The incident that night led to a brawl. Almost immediately, the surrounding compounds emptied out, and the streets filled with Yorubas and Hausas armed with machetes and guns. The fighting lasted four days and was ended only by the military occupation of Mushin. By then, more than a hundred residents had been killed, thousands had fled the area, and hundreds of houses had burned down.

Newcomers to the city are not greeted with the words "Welcome to Lagos." They are told, "This is Lagos"--an ominous statement of fact. Olisa Izeobi, a worker in one of the sawmills along the lagoon, said, "We understand this as 'Nobody will care for you, and you have to struggle to survive.' " It is the singular truth awaiting the six hundred thousand people who pour into Lagos from West Africa every year. Their lungs will burn with smoke and exhaust; their eyes will sting; their skin will turn charcoal gray. And hardly any of them will ever leave.

Immigrants come to Lagos with the thinnest margin of support, dependent on a local relative or contact whose assistance usually lasts less than twenty-four hours. A girl from the Ibo country, in the southeast, said that she had been told by a woman in her home town that she would get restaurant work in Lagos. Upon arrival, she discovered that she owed the woman more than two hundred dollars for transport and that the restaurant job didn't exist. The girl, her hair combed straight back and her soft face fixed in a faraway stare, told me that she was eighteen, but she looked fifteen. She is now a prostitute in a small hotel called Happiness. Working seven nights a week, with each customer spending three and a half dollars and staying five minutes, she had paid off her debt after seven months. She has no friends except the other girls in the hotel. In her room, on the third floor, the words "I am covered by the blood of Jesus. Amen" are chalked on a wall three times.

A woman named Safrat Yinusa left behind her husband and two of her children in Ilorin, north of the city, and found work in one of Lagos's huge markets as a porter, carrying loads of produce on her head. She was nursing a baby boy, whom she carried as she worked. She paid twenty cents a night for sleeping space on the floor of a room with forty other women porters. In two months, she had saved less than four dollars. Considering that the price of rice in Lagos is thirty-three cents per pound, it is hard to understand how people like Yinusa stay alive. The paradox has been called the "wage puzzle."