The government of Rio de Janeiro, has determined that walls be built around 13 slums located within the city. The building of the first one, surrounding the Dona Marta slum, has already begun. This is a theme that has been discussed in Rio de Janeiro since 2004, but what has changed since then is the reasoning behind the discussion. When announced in 2004, the walls were allegedly going to be an attempt to prevent the violence of the slums from spilling over to the rest of the city. The government´s proposal was considered a violation of human rights and a promotion of social apartheid by human rights activists and specialists in urban development, and the walls were never built. Now, concern with the environment is the main reason behind the initiative: the slums are allegedly invading the tropical forest (Mata Atlântica) that surrounds the city. Despite similar protests, the building has gone ahead.