Although visitors lured by the prospect of sun, surf, samba, and soccer may not perceive it, Rio de Janeiro is actually two very distinct cities. Some five million people live at or near sea level in what Brazilians describe as “the asphalt,” supplied with all the usual public services: subways, electricity, garbage collection, and at least a semblance of the rule of law. But another million or more Cariocas, as Rio residents call themselves, have been consigned to “the hillside,” a world of squatter settlements known as favelas, most of them indeed on hills, in which normal urban amenities like sewers and running water are scarce and a strikingly different system of laws, values, and conduct prevails.

Misha Glenny’s Nemesis: One Man and the Battle for Rio aims to give a sense of what life is like in those favelas, which, though they exist on the margins of every Brazilian metropolis, are especially visible and important in Rio, where they number more than one thousand and overlook Ipanema, Copacabana, and other elegant neighborhoods. The book’s arrival is timely: with the 2016 Summer Olympics scheduled to begin in Rio in August, the world’s attention is focused on the city, and Brazil’s success or failure in dealing with what it perceives as its biggest public security challenge, the threat of violence in favelas, is relevant not just to the country’s 200 million people, already grappling with the Zika virus and the biggest corruption scandal in Brazilian history, but also to the thousands of tourists, athletes, and journalists who will flock to Rio for the games.

Outsiders tend to think of the favelas as lawless places, but that’s not quite true. In City of God (1997), Paulo Lins’s novel about growing up in a violent housing project whose residents had been forcibly relocated from favelas the Rio authorities had razed, Lins describes a society based on consideração—literally “consideration.” In favela-speak the word is closer to “deference” or “respect.” Favelas do not offer even the pretense that all men are created equal, much less women. Instead there is a clearly defined hierarchy, at the top of which is a criminal don whose word and whims are law, rigorously enforced. Some of these chefões, or big bosses, are relatively benevolent or rational, in which case life for the working-class poor who make up most of the population in any favela can be tolerable. But others are violent, paranoid, and, though cunning, not particularly intelligent, which can make life miserable for the ordinary favelado.

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