Mathias participated in one of the most daring operations of the Civil War.
Grierson and his 1,700 horse troopers rode over six hundred miles through hostile territory (from southern Tennessee, through the state of Mississippi and to Union-held Baton Rouge, Louisiana), over routes no Union soldier had traveled before. They tore up railroads and burned crossties, freed slaves, burned Confederate storehouses, destroyed locomotives and commissary stores, ripped up bridges and trestles, burned buildings, and inflicted ten times the casualties they received, all while detachments of his troops made feints confusing the Confederates as to his actual whereabouts and direction. Total casualties for Grierson's Brigade were three killed, seven wounded, and nine missing. Five sick and wounded men were left behind along the route, too ill to continue.