They were built between 1179 (Naviglio Grande) and the 16th century (Naviglio Martesana) with the purpose of making Milan accessible from the Ticino and Adda rivers. These routes were not only used for commercial purposes but also for the transportation of marble used to build the Duomo Cathedral.
The History of Milan's Navigli Canals\n\n In 1457, the Naviglio della Martesana was built north of the city. The goal of the system was to connect Lake Maggiore, Lake Como, and the lower Ticino River. Leonardo da Vinci perfected the system on the behalf of Ludovico il Moro around 1482, improving navigation within Milan.