“We find that the Romans owed the conquest of the world to no other cause than continual military training, exact observance of discipline in their camps and unwearied cultivation of the other arts of war.”

De Re Militari (also Epitoma Rei Militaris), Book I, "The Selection and Training of New Levies"
Context: Victory in war does not depend entirely upon numbers or mere courage; only skill and discipline will insure it. We find that the Romans owed the conquest of the world to no other cause than continual military training, exact observance of discipline in their camps and unwearied cultivation of the other arts of war. Without these, what chance would the inconsiderable numbers of the Roman armies have had against the multitudes of the Gauls? Or with what success would their small size have been opposed to the prodigious stature of the Germans? The Spaniards surpassed us not only in numbers, but in physical strength. We were always inferior to the Africans in wealth and unequal to them in deception and stratagem. And the Greeks, indisputably, were far superior to us in skill in arts and all kinds of knowledge. (Book 1)