GUASTALLA, a strong town of Italy, in the duchy of Mantua, with the title of a duchy, remarkable for a battle between the French and Imperialists in 1734. It was ceded to the duke of Parma in 1748, by the treaty of Aix-la-Chapelle. It is seated near the river Po, in E. Long. 10. 38. N. Lat. 44. 55.