Guastalla , a town of Italy, in the province of Reggio, at the junction of the Cros-tolo and the Po, 18 m. N. E. of Parma; pop. about 10,000. It is well built, is surrounded by walls, and contains a cathedral, eight churches, a decayed castle, a public library, a theatre, a musical academy, and several educational and charitable institutions. It was founded by the Lombards, and during the middle ages passed successively into the hands of several Italian families and states. Subsequently it was made a fief of the German empire, and was raised to a duchy in 1021. By the treaty of Aix-la-Chapelle (1748) it was given to Don Philip of Spain, duke of Parma. In 1796 the French united it and the surrounding region to the Cisalpine republic. In 1805 Napoleon gave it to his sister Pauline, whose husband, the prince Borghese, was created duke of Guastalla, In 1815 the congress of Vienna allotted it, together with Parma and Piacenza, to the ex-empress Maria Louisa, upon whose death in 1847 it passed to the duke of Lucca, who in accordance with a previous arrangement ceded it to Modena, with which it was in 1860 incorporated into the dominions of Victor Emanuel.