On the march, each legionnaire was required to carry his weapons, armor, rations for up to a week, tent material, bedding, clothes and two posts for the camp wall (erected when the legion stopped for the night). This heavy load was often more than 80 lbs. of equipment, and earned the legionnaires the title "Marius' Mules" from the name of the general who reformed the army in the 2nd century BCE.
The Roman Army was proud of the fact that they were the best trained army in the World. From the ability to march more than twenty miles a day, and fight a battle immediately afterwards, to elaborate combat formations the legionnaires were the most combat ready force of the Ancient World. One of the more complex formations of the legionnaires was the Roman Testudo (tortoise) a defensive formation that allowed the legionnaires to advance in relative safety in the face of enemy missile fire.
The Roman Historian Livy said, the power of the Roman Army was based on three vital points: "Virtus-Opus-Arma" (Courage-Work-Weapons). As long as the Guardians of the Empire followed these truths the Empire was safe, when these failed so did the Empire.