The rape of Lucretia, according to Livy, was the fundamental "last straw" in the overthrow of the Etruscan King Lucius Tarquinius Superbus. The transition from the Etruscan monarchy to republic (510-509 BC) was not, however, a simple institutional change. In place of the King, the newly founded Republic relied upon its Senate, or patrician class families, to oversee the government and the election of various officials, including 2 shared power Consuls. This transformation from monarchy to representative style government, headed by the elite social class, would prove to have troubles of its own.
After the overthrow of the Tarquin dynasty, led by Junius Brutus, the ancient Romans avoided a true monarchal government for the remainder of their storied history (Even the later imperial government maintained forms of the republican system. While in practice it could be a system of absolute power for the Emperor, it was theoretically still checked by the Senate and other representative ideals.) This same Junius Brutus was later claimed as an ancestor by the Republican loyalist Marcus Brutus who was among the conspirators in the assassination of Julius Caesar, and shows the deeply rooted Roman aversion to Kings. It was the era of the Republic in which the great expansion of Roman civilization, power and structure set the path for European dominance. In these formative and expansive years, Rome was ruled by its Senate and its people's assemblies. The offices of power were divided among various elected officials to avoid the conglomeration of power and the re-institution of the monarchy.
These magistracies were in essence, a division of previous monarchal powers. The Romans instituted a constitution which would dictate the traditions and institutions of government for the Roman people. This constitution, however, was not a formal or even written document, but rather a series of unwritten traditions and laws. Deeply rooted in pre-Republican tradition, it essentially maintained all the same monarchal powers and divided them amongst a series of people, rather than in one supreme ruler.
Patricians and Plebeians
Discontent and political upheaval lay ahead for the fledgling Republic, since the new constitution was flawed and exclusive in nature for the general population (plebeians). Rome was surrounded by powerful external enemies, including its former Etruscan rulers, and Patrician (the hereditary aristocratic families) in-fighting with each other and the plebeian (common people) class was an immediate source of difficulty. The Romans developed a complex client system, where aristocratic families pledged allegiance and voting support to other powerful families. In exchange for political appointments and advocating of various agendas, some power groups were able to subvert the state and the will of the masses for personal gain.
The words Patrician and Plebeian have taken on different connotations of wealthy and poor in modern English, but no such distinction existed in Roman times. The two classes were simply ancestral or inherited. A citizen's class was fixed by birth rather than by wealth. Patricians monopolized all of the political offices and probably most of the wealth in the early Republic, but there were many wealthy plebeians, and conversly many patrician families had little claim to wealth or prestige other than their family heritage. The relationship between the plebeians and the patricians sometimes came under intense strain, as a result of this exclusion from political influence. In repsonse, the plebeians on several occasions, abandoned the city leaving the patricians without a working class to support their political whims.