Senigallia (sānēgälˈlyä) [key], city (1991 pop. 41,144), in the Marche, central Italy, on the Adriatic Sea. It is a port, a seaside resort, and an industrial center. Manufactures include textiles, processed food, and construction materials. Made a Roman colony in the 3d cent. B.C., it was later (6th cent. A.D.) one of the cities of the Byzantine Pentapolis. Although included in the territories donated (8th cent.) by Pepin the Short to the popes, it became (12th cent.) a free commune and then was a papal fief under various rulers. Cesare Borgia had several rebellious lords slain there (1502). The city has walls and a castle dating from the 15th cent. and two Renaissance churches.