The gladius, or Hispanic Sword as they called it, is the iconic short sword of the Roman army. It was adopted from the clans and tribes that lived in Spain. These tribes of Iberians, Celts and a large mixed group called Celtiberians, created hill forts and cities. Tribes of these three groups frequently warred with each other, developing an effective style of warfare but remaining politically divided. During the Second Punic Wars when Rome and Carthage fought to destroy each other and dominate Spain the great Roman General Scipio Africanus took a liking to this "Spanish Sword" and began equipping the legions under his command with the weapon. Scipio then defeated Hannibal, the greatest general of Carthage, at the battle of Zama ending the Second Punic War, this victory has often been credited to his use of the gladius as well as too the defection of a large amount of Numidian cavalry to the Roman cause.
In combat the gladius could be used for stabbing or slashing, although it was primarily used for stabbing. In the crush of battle that often occured when two forces pressed against each other the gladius shined. It was ideal for stabing in these conditions where longer weapons became useless due to the lack of room for long slashing swords and thrusting spears. Roman legionaries constantly practiced with their weapon of choice, learning to make thrusts into vulnerable areas of their enemies such as the groin or neck.
The gladius served the Romans as the main Roman weapon through the rest of the Roman Republic and partially through the Empire (4th century BC - 3rd century AD). The Legions that poured from Rome to conquer the Mediterranean world held this weapon in their hand. The famous Roman weapon delivered victory for to the Romans for 600 years, from the British Isles to Egypt, however, warfare was changing in the third century AD and the Roman's had to change their weapons too. In the late empire new threats appeared from the Asian steppes and darker Europe, mounted warriors like the Huns and Goths required a different army to repel. The Romans began to focus more of their military power to counter mounted warriors, archers and cavalry started taking on greater importance. The old role of the heavy infantry shifted as well, it became critical to defend the infantry from cavalry and so the Romans adopted longer weapons for their infantry. At first a longer sword, called the Spathea was employed, but over time the main weapon of the Roman infantry returned to where it had begun; the spear.
The pilum is the heavy javelin used by the Roman legionnaires. Along with the sword, the pilum was one of the main weapons of the Roman military and provided each man with mobile, short ranged artillery ability. It is perhaps one of the biggest reasons for Roman dominance of the ancient world, along with the full body shield and gladius. While Rome’s star was just raising the Mediterranean world was dominated by the Macedonian style phalanx. These ponderous formations presented a wall of spikes to any would be attacker and since the time of Alexander the Great (almost two hundred years earlier) the Macedonian Phalanx impaled and skewered it's enemies in a relentless march forward. However, when the Roman Legions faced off against this force they able to exploit gaps in the phalanxes formation caused by uneven ground and the effects of the pilum.
In the Battle of Pydna (168 BC) between Rome and the Macedonian Antigonid dynasty, the Romans although a first awed by the power of the phalanx, were able to smash it. The balance of power was forever changed in Mediterranean and Rome was shortly to become its new master.
A pilum is essentially a heavy javelin featuring a long thin iron shank (neck) and heavy shaft. The relitvely thin iron shank, with its barbed tip, gave the pilum its extraordinary ability; it was armor piercing. The weight of the shaft and a weight in the shape of pyramid or ball would then punch the shaft through enemy shields and armor. The 2 foot long (60 mm) shaft was designed to be long enough to punch through a shield and into the man behind it. Even if the shaft didn't connect with the man holding the shield then the pilum had the added benefit of rendering the shield useless due to the large javelin poking through and hanging from the front of it. Many of unarmored Germanic and Celtic barbarians were forced to discard their shields due to the pilum, a near death sentence for them on the battle field. An added benefit of this design was that the force of the impact would often bend the shank, causing it to be unusable and saving the Romans from having them thrown back at them.
Roman soldiers typically carried two pilum and they would throw them as they charged their enemies to cause death, discarded shields and confusion among the ranks of their enemies. Modern testing has revealed that a pila (singular for pilum) can be thrown 98 feet but it probably had an effective range of between 50-66 ft. A typical Roman strategy would have been to unleash their second pilum from a distance of only about 15-20ft and then to follow up with their swords, giving their enemy no time to recover. The barbarians that continually assaulted the Romans from the North preferred to open battles with a mass, furious charge of great power. To counter this Romans would throw their pilum into the charging hoard, the impact of would deliver a counter shock, blunting the enemies force before it collided with the Roman battle lines.
Additionally, the Romans found the pilum to be an effective anti-cavalry weapon. Julius Cesar used this tactic to great effect when he ordered a cohort of his legionnaires to use their pilum to stab at the faces of the cavalry of Pompeii during the first Roman civil war in the first century BC.
The origins of the pilum is most likely a result of the Samnite Wars (343-290 BC). These decades long conflicts proved to be a tough trial for the Roman Republic, and they suffered several humiliating and disastrous defeats at the hands of the hill tribes called Samnites. The Samnites fought in a loose order, peppering their enemies with javelins while the Romans fought in a hoplite style, utilizing shield wall (phalanx) tactics. However the rough ground of the hill tribes proved to be unfavorable to the use of phalanx tactics and the ever adaptive Romans changed both their strategy and weapons, adopting a looser "checker board" formation and employing heavy javelins. (To learn more about these tactical changes see Roman Military or Ancient Weapons).
Hasta, a Latin word meaning spear, was the first and last main Roman weapon. Hastae is the plural form of hasta. A hasta was about 6.5 feet (2 m) long with an iron head and a shaft typically made of ash. The earliest Rome forces fought in a phalanx style like Greek warriors using spears, however, during the Republic a switch was made to using three lines. The first two lines employed swords while the third, and final battle line, was made out of veterans using hastae. Eventually all legionaries where equipped with swords during the military reforms and standardizations of Gaius Marius (157-86 BC).
During the late empire, starting in the 3rd century AD, the Romans infantry began to switch back to using the Hasta. The reason for this is most likely the changing nature of warfare at the time, particularly the ascendancy of cavalry. The hasta proved to be the most effective weapon against the rampaging horsemen that devastated the late empire and it was eventually reinstated as the main weapon of the Romans.
Other Roman Weapons
The above weapons are the main weapons of the Roman heavy infantry man, however, the Romans employed a number of other weapons as well. For example the pugio was a dagger used as a sidearm by the roman legionnaires. It featured a wide leaf shaped blade and was about 9.5" - 11" long. During the first and second centuries AD, the spathea became a common weapon of choice. The spathea was a longer sword then the gladius, first used by the Roman cavalry but adopted by the infantry. During the late empire the legionaries began to carry the Plumbata, this was a weighted throwing dart. Six plubata could be secured to the back of a shield and they had a greater range then a javelin. Lead weights on the plumbata also gave it good penetration. These weapons proved extraordinarily effective for the Romans, allowing their heavy infantry to operate effectively as their own archers. It is also likely that legionaries would employ slings at times.
Besides heavy infantry the Roman armies fielded other specialized troops. Their light infantry, called velites, employed light throwing javelins. These javelins had greater range then the pila, but lacked their punch. Roman archers, called the sagittarius, their normal weapon was the composite bow, made of horn and wood, and held together with sinew and hide glue. Reinforcing laths for composite bows are found throughout the Roman territory. Roman auxiliaries used a wide range of weapons, whatever the weapons of their particular tribe were what they went into combat with. These weapons could be anything from Balearic slings to Frankish throwing axes; however, I wouldn't consider these to truly be Roman weapons.