An unofficial policy of tolerance in Lima, Peru, led to the widespread occupation of peripheral land during the latter half of the twentieth century. Barriadas, as these neighbourhoods were called, provided a way for low-income settlers to gain mostly free access to land and build at their own pace and in accordance with their capacities. While serving a clear need, such neighbourhoods were largely unofficially planned, self-improvement efforts moved slow and were resource-dependent and construction was sometimes of poor quality. Efforts at regularization and improvement that followed settlement proved expensive and time-consuming when undertaken by settlers or government.
While providing shelter to large numbers of low-income Peruvians, the proliferation of hundreds of self-help neighbourhoods fuelled low-rise sprawl that pushed back the edges of Lima and gradually consumed much of the buildable land on the periphery. This pattern contributed to a sharp reduction in the supply of land affordable to low-income households, especially land located within a reasonable distance of work opportunities. As land became scarcer, once low-density settlements accommodated increasing numbers of new residents in a process of vertical growth and densification, sometimes resulting in conditions of overcrowding. Faced with inflated land costs and little remaining free land, new arrivals or poorer households toward the end of the century were hard pressed to purchase their own land. This evolution has been one of the factors leading to the occupation of the precarious areas that remain at the turn of the century.