The city was the protagonist of a progressive urbanization that led to a considerable expansion of the population center. At the origin of this phenomenon was the birth of many industries that attracted workers from different parts of Italy. As can be seen from the demographic evolution, between 1871 and 1921 the population of Legnano quadrupled. Due to the need for water, the mussel industries born in the 19th century sprung up along the shores of the Olona. As a result, the new residential districts have occupied the free areas beyond the river valley.