Roman Empire, political system established by Rome which lasted nearly five centuries. Historians generally date the start of the Roman Empire to 27 BC. 500 BC, when the Roman Senate gave Gaius Octavius ​​the name Augustus and he became undisputed emperor after years of bitter civil war. At its peak, the empire included lands spread across the Mediterranean world. Rome had first expanded to other parts of Italy and neighboring territories during the Roman Republic (509–27 BC), but had achieved wider conquests and consolidated political control of these lands during the empire. The empire lasted until Germanic invasions, economic decline, and internal unrest in the 4th and 5th centuries ended Rome's ability to dominate such a huge territory. The Romans and their empire gave cultural and political shape to the later history of Europe, from the Middle Ages and the Renaissance to the present day. In 44 BC, Gaius Julius Caesar, the Roman ruler who ruled the Roman Republic as a dictator, was assassinated. Rome descended into more than a decade of civil war and political upheaval. After Caesar's heir, Gaius Octavius ​​(also known as Octavian), defeated his remaining rivals, the Senate in 27 BC. AD proclaimed him Augustus, that is to say the exalted or the saint. Augustus thus established the monarchy known as the Roman Empire. The Roman Republic, which had lasted nearly 500 years, was dead and was never to be reborn. The empire would last another 500 years until 476 AD (see Ancient Rome). Emperor Augustus reigned from 27 BC to 14 AD and ruled with absolute power. He restored political and social stability and launched two centuries of prosperity called the Roman Peace (Pax Romana). Under his rule, the Roman state began to transform into the largest and most influential political institution in European history. During the first two centuries CE, the empire prospered and added new territories, including ancient Britain, Arabia, and Dacia (present-day Romania). People from the Roman provinces flocked to Rome, where they became soldiers, bureaucrats, senators and even emperors. Rome has become the social, economic and cultural capital of the Mediterranean world. Despite the focus on tyrannical and often vicious rulers like Emperors Caligula and Nero, most emperors ruled reasonably and competently until military and economic disasters caused political instability in the 3rd century AD. The Roman Empire encompassed a huge amount of territory, but also allowed people from many different cultures to maintain their heritage into modern times.