Unable to make any significant gains in action, Pyrrhus deployed his war elephants, held in reserve until now. The Roman cavalry was threatening his flank too strongly. Aghast at the sight of these strange and brooding creatures which none had seen before, the horses galloped away and threw the Roman legion into rout. (The Romans subsequently called elephants , after the location of this first encounter.). Pyrrhus then launched his Thessalian cavalry among the disorganized legions, which completed the Romans' defeat. The Romans fell back across the river and Pyrrhus held the field.