INSTEAD of the long spear of the Grecian heavy-armed warrior, the soldiers were equipped with short throwing-spears, which were used in a way analogous to modern machine-gun fire. As soon as the enemy came within range, these spears were aimed at their shields. The point penetrated deep into the shield, but the shaft, being of soft metal, bent so that it could not be pulled out and thrown back straight. The soldiers then advanced on the embarrassed enemy with the short and handy stabbing sword. So thorough was the discipline that after each day's march a mound of earth was dug round the camp. This was crowned with a palisade of stakes, and kept away surprise attacks. The Roman soldier, with his sword and spear, his entrenching tool and his stakes, and his rations for seventeen days, must have carried as heavy a kit as British soldiers did in the Great War. The legions were divided into units called centuries, each in command of a centurion, who combined the duties of a sergeant-major and a captain. The higher officers consisted of the Consul and his picked staff of young nobles. In the fourth century, the inconvenience of making a Consul leave the army at the end of his year of office led to the institution of the proconsulship, which enabled him to stay in command for another year. The battle between the Indo-European and the Semite which had been fought in the Eastern Mediterranean, was now renewed in the West. Commerce and trade had developed with the growth of Empire, but the Roman merchants, anxious to extend their operations overseas, found the way barred by Carthage, which controlled the corn trade of North Africa, the silver mines of Southern Spain, and the carrying trade of the whole Mediterranean. She even had commercial posts on the Atlantic coast of Africa, and allowed no foreign ship to pass through the Straits of Gibraltar. Carthaginian colonies in Sardinia and Corsica and the west coast of Sicily had existed for centuries. Peaceful expansion for Rome seemed impossible. Therefore she turned to war, where the chances were good. The Carthaginian government was an oligarchy of wealthy traders, relying on a mercenary army and navy, not on land-owning citizen farmers, hardened by two centuries of war.