an ancient Italic Sabellian tribe in central Italy.

During the Samnite Wars in the fourth century B.C., the Marsi fought on the side of the Samnites against the Romans. From 304 to 90 B.C., the Marsi were allied with the Romans. In the Social War of 90 (or 91) to 88 B.C., however, the Marsi were the first to rise up against Rome, and they played a leading role in the war (hence, the war is also called the Marsian War).