History of the Constitution of the Roman Republic
The history of the Constitution of the Roman Republic is a study of the ancient Roman Republic that traces the progression of Roman political development from the founding of the Roman Republic in 509 BC until the founding of the Roman Empire in 27 BC. The constitutional history of the Roman Republic can be divided into five phases. The first phase began with the revolution which overthrew the Roman Kingdom in 509 BC, and the final phase ended with the revolution which overthrew the Roman Republic, and thus created the Roman Empire, in 27 BC. Throughout the history of the republic, the constitutional evolution was driven by the struggle between the aristocracy and the ordinary citizens.
Roman Empire
Rome had begun expanding shortly after the founding of the republic in the 6th century BC, though it did not expand outside the Italian peninsula until the 3rd century BC. Then, it was an "empire" long before it had an emperor. The Roman Republic was not a nation-state in the modern sense, but a network of towns left to rule themselves (though with varying degrees of independence from the Roman Senate) and provinces administered by military commanders. It was ruled, not by emperors, but by annually elected magistrates (Roman Consuls above all) in conjunction with the senate. For various reasons, the 1st century BC was a time of political and military upheaval, which ultimately led to rule by emperors. The consuls' military power rested in the Roman legal concept of "imperium", which literally means "command" (though typically in a military sense). Occasionally, successful consuls were given the honorary title "imperator" (commander), and this is the origin of the word "emperor" (and "empire") since this title (among others) was always bestowed to the early emperors upon their accession.
Rome suffered a long series of internal conflicts, conspiracies and civil wars from the late second century BC onward, while greatly extending its power beyond Italy. This was the period of the Crisis of the Roman Republic. Towards the end of this era, in 44 BC, Julius Caesar was briefly perpetual dictator before being assassinated. The faction of his assassins was driven from Rome and defeated at the Battle of Philippi in 42 BC by an army led by Mark Antony and Caesar's adopted son Octavian. Antony and Octavian's division of the Roman world between themselves did not last and Octavian's forces defeated those of Mark Antony and Cleopatra at the Battle of Actium in 31 BC, ending the Final War of the Roman Republic. In 27 BC the Senate and People of Rome made Octavian "princeps" ("first citizen") with proconsular "imperium", thus beginning the Principate (the first epoch of Roman imperial history, usually dated from 27 BC to AD 284), and gave him the name "Augustus" ("the venerated").