Pilum: The pila (plural form) were quite unique in design. These javelins were designed to warp after impact, so they would drag down an enemy's shield, sometimes pinning two of them together. The average pilun was 1.8 meters long. It had a barbed iron shaft connected to the wooden pole in a weighted socket. A lead ball weight was added to further increase the throwing distance in the late half of the 2nd century AD. Pilum were used until the late empire.
Hasta: The hasta was the Roman trusting spear. It was carried by the units called triarii in Republic times. Marius military reforms made the pilum the standard spear carried by all legionaries.
Gladius: The Romans patterened their short swords after those of the Spanish Celts. The historian, Polybius, says they were introduced into the army during the second Punic War. This sword was intended as a thrusting weapon. This was the best way to use a sword in tight formation. Using the sword in a slashing motion would cause the soldier to open his side to attack. The gladius was replaced by the traditional long swords of the barbarians in the late empire. The below image is of the Pompeii type.
Archaeologists have catagorized these swords into three main types. The oldest, "Mainz" pattern had a blade 20 - 22 in. long, about 2.5 - 3in. wide. The edges curved inward at mid length of the blade. This was the blade carried by the soldiers of Caesar's time up till Tiberius. The later "Fulham" and the "Pompeii" types had edges which were parallel. The Fulham pattern was jus as long as the "Mainz." The blade started slightly wider at the hilt, sloping sharply to a 2 in. width for the rest of the length to the tip. The "Pompeii" had a shorter blade length, 18 - 22 in., was typically 2in. wide, and had completely parallel edges.
See photo of a Fulham sword on the British Museum website.
Spatha: The was the sword used by the cavalry. The blade was much longer than the galdius and was used for slashing. The large numbers of barbarians serving in the legions used the spatha in the late empire. It was ideal because the spatha did not require the same skill and training needed to properly wield a gladius.
Pugio: The legionaries carried a dagger starting in the 2nd or 1st centuries BC. During the rein of Augustus the gladius was carried on one belt and the pugio hung on another. By the 2nd century AD daggers were no longer issued.
Lancea: This repalced the pilum as the primary weapon of the 3rd century AD on. It was a thrusting spear.
Veruta: This was the throwing javelin of the late empire.
Plumbatae or Mattiobarbuli: These were hand-thrown lead weighted darts carried by the infantry. They were rather expensive to produce, but they allowed the infantry to effectively double as missile troops.References:
1. Bishop and Coulston. Roman Military Equipment, 2nd Ed., Oxbow, 2006. p. 98-100.
2. Connolly, Peter. Greece and Rome at War,. Greenhill Books 2006.