During the post-war economic boom , a large wave of internal migration ( especially from rural areas of Southern Italy ) moved to Milan . The population grew from 1.3 million in 1951 to 1.7 million in 1967 . During this period , Milan was largely reconstructed , with the building of several innovative and modernist skyscrapers , such as the Torre Velasca and the Pirelli Tower . The economic prosperity was , however , overshadowed in the late 1960s and early 1970s during the so-called Years of Lead , when Milan witnessed an unprecedented wave of street violence , labour strikes and political terrorism . The apex of this period of turmoil occurred on 12 December 1969 , when a bomb exploded at the National Agrarian Bank in Piazza Fontana , killing seventeen people and injuring eighty-eight
a bomb
Piazza Fontana bombing
Milan