This study examines in depth the pugio (pl. pugiones), a short dagger-sword and one of the weapons of choice of the Roman army - it was the weapon that killed Julius Caesar. Its rich decoration and the use of precious metals have given it legendary status, which has been enhanced by a scarcity of literary sources and the lack of a clear explanation of its function or the specific use soldiers made of it. This work tries to fill this gap, basing its finds exclusively on undisputed data and sources. This study of the pugio takes us through the history and evolution of the Roman army itself.