Rome didn't become the most powerful empire in the ancient world without waging serious wars. At the height of the ancient Roman empire, it was the world's most accomplished -- and feared -- military presence. Rome acquired nearly 250,000 square miles (402,336 square kilometers) of land stretching from the Italian peninsula to Spain, Gaul and Carthage.

But Rome didn't begin as a military superpower. During the Punic Wars, Rome was forced to conduct naval warfare for the first time. Ancient Rome didn't have a proper naval fleet, so the soldiers replicated a ship that the Carthaginians had abandoned. The Romans went on to defeat Carthage using their own interpretation of naval warfare -- storming the enemy's ships by way of a plank and then engaging in hand-to-hand combat.

Victory wasn't a sure thing for the ancient Romans, though. Because ancient Roman battles were led by men with more government experience than military wiles, the Romans made some foibles on the battlefield -- particularly when they were up against one of their greatest enemies, the Carthaginian general Hannibal. Until the Roman general Scipio masterminded troop maneuvers and strategies that matched Hannibal's, the Romans were constantly beaten down by the Carthaginians. Scipio countered Hannibal's elephant warfare with Roman troop corridors on the battlefield, and this marked a turning point in ancient Roman battles.

Romans recognized the importance of commissioning professional soldiers to wage war; using its citizens was bankrupting the empire. What's more, with countless soldiers slaughtered in battle, Roman families were in a near-constant state of worry and grief. That changed with the general Marius, who drafted men to enter a state of military servitude that, upon completion, would be rewarded with a parcel of land. With the advent of the professional soldier, there was no stopping the Roman empire in its process of expansion and the exponential increase of its wealth.