The Roman armies that invaded Britain in 55 BC and 43 AD were primarily composed of foot soldiers called Legionaries.
During the course of the Roman Empire, the weapons and equipment of the standard foot soldier underwent a number of changes. However, despite a nearly one hundred year time gap, the soldiers that fought during the two invasions of Britain would have been similarly equipped.
Roman Weapons
Pilum (javelin): The most commonly depicted weapon of the Roman Legionaries was a heavy javelin called a pilum. It was around six feet long and toped with a metal shank leading to a heavy pyramidal point. The Pilum was a short-range missile weapon whose heavy head could punch through enemy shields and armor. During battle the Roman front lines would heave their pilums just before charging into the enemy. Even if not fatal, the heavy pilums could cause confusion and disorder by pinning enemy shields together or forcing them to be discarded because the javelin could not be extracted.
Gladius (sword): To the Romans, the word "gladius" simply meant "sword" and was not a specific type. During the invasion of Julius Caesar the Legionaries probably carried medium length (64-69cm) straight edged swords that tapered to a point. By the invasion of Emperor Drusus this had likely been replaced by the shorter, classic Roman sword (40-56cm in length). The sword was the primary fighting weapon of the Legionary and was usually used to thrust at exposed areas of the enemy.
Roman Armor
Scutum (Shield): During the first invasion, the scutum was a large (1.25 meters high) oval that curved slightly inward on either side. It was made of laminated wooden planks surrounding a heavy metal boss. The shield could be used offensively to bash opponents and knock them off balance. Also, Legionaries in close formation could lock their shields together both in front and above them to a form a compact, armoured formation called a testudo (tortoise). By the second invasion the shield had become a slightly curved rectangle but its function remained exactly the same.
Armor: By far the most common type of armor during this period would have been chain mail. The Roman version usually consisted of a mail tunic, doubled over at the shoulders and reaching to about midway between the hips and knees. The arms were left completely uncovered. In some cases additional plates may have covered the chest. Armor made of metal scales was probably also in use, but was inferior in terms of both weight and protection. By the second invasion, it is possible that some units were equipped with new armor made of wide metal bands, but this would have been uncommon.
Helmet: Legionary helmets were usually bronze bowls with large guards reaching down over the ears and cheeks. It also had a protective brow ridge as well as a flared out back to protect the back of the neck.
The standard arms, armor, and equipment carried by a Roman Legionary weighed in the vicinity of 65-70 lbs.