4 – Weakened Military
At its peak, the Empire stretched from the Atlantic Ocean to the Euphrates River, but its sheer size proved to be a burden. Although the Romans created an excellent transport network, they still found it tough to communicate. Naturally, Rome created a vast array of enemies when expanding its empire, so it was constantly under attack from different tribal peoples eager to seek revenge.
Recruiting sufficient troops and sending them to different parts of the empire to quell uprisings started to take its toll. In the 2nd Century AD, Emperor Hadrian built his famous wall in Britain as a means of keeping the enemy at arm’s length. The sheer cost of constant recruitment and military upkeep meant Rome ultimately stopped leading the field in technological advancements.
Gaius Marius’ changes towards the end of the 2nd Century BC significantly contributed to the growth of the Roman army. It became one of the most awesome and well-organized fighting units in the world and was both feared and respected by its enemies. Over time, however, the entire makeup of the army changed dramatically. One method of getting Romans to enlist in the military was by offering a competitive salary. Ultimately, the empire started to struggle to maintain a good rate of pay, so fewer Romans were willing to join.
Emperors such as Diocletian and Constantine felt it necessary to hire foreign mercenaries to swell the ranks of the imperial army. These ‘barbarians’ could be recruited for lower pay and the promise of Roman citizenship for service. It got to the point where Romans in the army used the word ‘barbarus’ instead of ‘soldier.’ Eventually, the army was filled with Germanic Goths and other barbarians.
While these new recruits were exceptional warriors, they had zero loyalty to the empire. In fact, they increasingly began to turn against their Roman counterparts. The infiltration of mercenaries led to disorganization as the army no longer functioned like the well-oiled machine of lore. The Barbarians gained sufficient knowledge of Roman military tactics to use this information against their enemies. A significant number of the Barbarians that sacked Rome once fought in the Roman army.