The government of Rio de Janeiro is building concrete walls to prevent sprawling slums from spreading farther into the picturesque hills of this world-famous tourist destination.

Construction has begun in two favelas, or shantytowns, in the southern districts of Rio de Janeiro, a government spokeswoman told Reuters. One of the two is Morro Dona Marta, which police occupied in November to control crime and violence caused mostly by rival drug gangs.