Many large housing estates were built in Marseille in the 1960s and 1970s to cope with massive immigration. They were mainly built in the northern part of the city, which urbanized very quickly. Today considered underprivileged, the northern districts are affected by violence, drug trafficking, and a high unemployment rate. However, they are not the only ones to present large complexes and high buildings, residential towers having also been built in the old districts of the city center and sometimes above some traditional fishermen's houses.