The post-Republican period of the ancient Roman civilization, known as the Roman Empire, was characterized by a government headed by emperors and large territorial holding around the Mediterranean Sea in Europe, Asia, and Africa. The Roman Empire was the

The post-Republican period of the ancient Roman civilization, known as the Roman Empire, was characterized by a government headed by emperors and large territorial holding around the Mediterranean Sea in Europe, Asia, and Africa. The Roman Empire was the largest empire of the Classical Antiquity period, and one of the largest in world history covering 6.8 million square kilometers. It was also among the most powerful economic, cultural, political and military forces in the world holding sway over 21% of the world's entire population during that time period. The longevity and vast reach of the Empire provided a lasting influence of Latin and Greek language, culture, religion, inventions, architecture, philosophy, law, and government on future descendants. There are three reasons the Roman Empire became so powerful.

The first reason was their large armies that occupied the lands of other countries. These armies were made up of captives forced to serve in the army and by the professional soldiers of the Imperial Roman army. Professional soldiers volunteered for 20 years of active service followed by five years of reserve duty. This was a definite shift from the material of the former republic in which an army of conscripts exercised their responsibilities as citizen to protect their homeland in specific campaigns against specific threats, whereas Imperial Rome's army was a full-time career.
The second reason for the Roman Empire's rise to power was the power held by the monarchs. This state of absolute monarchy began with Diocletian and endured until the fall of the Western Roman Empire in 476 CE. The authority of the emperor was based on the consolidation of several of the republican offices. The emperor had powers of inviolability of the tribunes of the people, authority of the censors to manipulate the hierarchy of Roman society, central religious authority as Pontifex Maximus, the right to declare war, ratify treaties, and negotiate with foreign leaders. These functions were clearly defined during the Principate, but over time the emperor's powers became less constitutional and more monarchial creating the dominate.

Finally, the high taxes placed on their empire helped to make the empire richer. The taxes an individual paid ranged from 2 to 5 percent of the gross product. The bewildering tax code involved a complicated system of direct and indirect taxes as well as taxes paid in cash and some paid in kind. The taxes might be specific to a province, property, or in effect for a limited time. The Roman Empire justified their tax collection as a necessary cost to maintain the military; however, taxpayers sometimes received a refund if the army obtained a surplus of booty. Less monetized areas that were unable to pay their taxes in cash were allowed to pay in-kind especially if they could supply grain of goods to the army camps.