Piacenza (ancient Placentia), city, northern Italy, capital of Piacenza Province, in Emilia-Romagna Region, near the confluence of the Po and Trebbia rivers, on the Lombard plain. It is a commercial and manufacturing center, with natural gas and oil-refining facilities and factories engaged in the production of cement, processed food, plastics, leather goods, and agricultural implements.

Founded by the Romans in 218 bc, Piacenza has many fine churches, including a cathedral in the Lombard-Romanesque style (1122-33). During the 12th and 13th centuries it was an important member of the Lombard League. From 1545 to 1731 it was ruled by the Farnese family, which left its imprint on the architecture of the city. Population (2007 estimate) 99,625.