Guastalla (gwästälˈlä) [key], town (1991 pop. 13,354), Emilia-Romagna, N Italy, on the Po River. It is an agricultural and industrial center. Probably founded in the 7th cent., Guastalla was held by various lords and in 1539 was bought by Ferrante Gonzaga of Mantua. It was made a duchy in 1621. After the Guastalla branch of the Gonzagas became extinct in 1746, the duchy passed (1748) to Parma. In 1806, Napoleon I conferred Guastalla on his sister, Pauline Borghese, but it later reverted to Parma.