As Rome developed into a veritable power on the Italian peninsula and later throughout Europe, so too did the famous Roman Republic, based around the Roman Senate. But Rome’s first governmental system was monarchial. The Roman king had absolute power, referred to by ancient Romans as imperium.
He served as the creator and enforcer of laws, the leader of the military, the head of the judiciary, and as the chief priest among his people. Even in the beginning, however, the Roman monarch was limited by a constitution.
The Roman monarchy was patriarchal, like the Roman society. The king had supreme power over his "family" but was also responsible for their welfare. A weak senate and assembly advised the king and had the power to approve the appointment of a king.
In many ways the Senate, made up of wealthy and respected Roman leaders and elders, known as patricians, acted in a fashion similar to the U.S. Supreme Court; they judged the constitutionality and correctness of the king’s actions but rarely acted against his wishes.
The Assembly, on the other hand, was made up of male citizens of Rome whose parents were native Romans. It was the institution that represented the majority of the population, known as plebeians, and granted absolute authority to the king. In the sixth century b.c.e. the Roman monarchs were Etruscans from a powerful empire based in northern Italy who briefly controlled Rome.
When an Etruscan prince from the ruling family, known as the Tarquins, raped the wife of a prominent patrician, Rome rebelled and expelled the Etruscans. The reign of the Roman Republic began following the expulsion. Two consuls inherited monarchial power, patricians elected to serve as head of state for one year.
Although the consuls held imperium, they were severely limited by annual reelection, by the ability to veto the actions of the other consul, and by an empowered Roman Senate.
These constraints caused conservative governance, which proved harmful during extended military conflicts, leading to the creation of proconsuls who were consuls permitted by the Senate to extend their term of office. Below the consuls were financial officers known as quaestors, military officers known as praetors, and accounting officers, known as censors.
Even though imperium was separated by different branches of Roman government, it was concentrated in the hands of patricians. In response to this reality, the plebeians struggled to gain political power and equality. In 450 b.c.e., the Law of Twelve Tables resulted from the class struggle, codifying Roman law.
By 445 b.c.e. plebeians gained the right to marry a patrician and in 367 b.c.e. gained the right to run for the consulship and other positions, leading to the Licinian-Sextian Laws, which required one consul to be plebeian. Julius Caesar’s assumption of power led to the establishment of the Roman emperorship, known as the princeps, in 44 b.c.e.
For the following half-millennium, Roman emperors controlled a vast European and Mediterranean empire, which slowly eroded. In an attempt to prevent the collapse, Emperor Diocletian split the empire in two and based it in Rome and Constantinople in 285 b.c.e., ultimately leading to a full split in 395 b.c.e. and Rome’s fall in 476 b.c.e.