The Roman Legion was a term that came to represent the vast military system that enabled the Roman empire (see Ancient Empires - Rome) to conquer and govern the ancient world of Europe (including Britain), south-central Asia and the Middle East, and North Africa. Centered on Rome, it was unquestionably the sole military superpower of its day, all connected by an elaborate system of Roman Roads.
A legion was the largest unit in the ancient Roman army, composed of infantry and cavalry. At full strength, such a division could consist of up to 6,000 soldiers. Each legion was divided into cohorts of 600 men, and each cohort was further divided into centuries of 100 men. A century was commanded by a centurion.
In the early empire, there were 28 formally-established legions, however as the empire expanded the military establishment grew along with it. Each legion developed its own traditions and standards (flags and insignia). The 10th Legion was apparently a favorite of Julius Caesar in the earlier years, and after the destruction of Jerusalem (see The Fall of Jerusalem In 70 A.D.) it, under the command of the future emperor Titus (see New Testament Roman Emperors), was the primary force that took Masada.
Roman weaponry for individual troops consisted of a helmet, some version of body armor, a large curved shield, and a now-famous Roman "short-sword." Peter was carrying one when The Messiah was arrested The Fateful Night, and he used it to slice off Malchus' right ear (John 18:10) (some are of the belief that the bold Peter, while attempting to defend The Lord from the mob, actually swung the weapon with the intent to do much more serious damage, but Malchus dodged sufficiently so that the sword only took off his ear as it grazed his head). Most also carried a heavy javelin that could penetrate enemy shields and armor quite effectively at a considerable distance. It was the last item, the javelin (or spear), that actually killed the nearly-dead Jesus Christ (see How Did Jesus Christ Die?), to fulfill the requirement of "His shed blood" - "But one of the soldiers pierced His side with a spear, and at once there came out blood and water." (John 19:34 RSV)
Fact Finder: Will the Roman soldier who pierced Jesus Christ with a javelin see Him again one day?
Revelation 1:7
See also The Return Of Jesus Christ