Roman Empire, political system established by Rome that lasted for almost five centuries. Historians usually date the beginning of the Roman Empire to 27 BC, when the Roman Senate gave Gaius Octavius ​​the name Augustus and he became the undisputed emperor after years of bitter civil war. At its height the empire encompassed lands throughout the Mediterranean world. Rome initially expanded into other parts of Italy and neighboring territories during the Roman Republic (509-27 BC), but made broader 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 vast territory. The Romans and their empire gave cultural and political shape to the subsequent history of Europe from the Middle Ages and the Renaissance to the present day. In 44 BC Gaius Julius Caesar, the Roman leader who ruled the Roman Republic as a dictator, was assassinated. Rome was plunged into more than ten years of civil war and political upheaval. After Caesar's heir Gaius Octavius ​​(also known as Octavian) defeated his last rivals, the Senate in 27 BC proclaimed him Augustus, that is, the exalted or saint. In this way Augustus established the monarchy that became known as the Roman Empire. The Roman Republic, which had lasted almost 500 years, was dead and would never come back to life. The empire lasted for another 500 years until 476 AD (see Ancient Rome). Emperor Augustus reigned from 27 BC to 14 AD and ruled with absolute power. He re-established political and social stability and began two centuries of prosperity called the Roman Peace (Pax Romana). Under his rule the Roman state began its transformation into the largest and most influential political institution in European history. During the first two centuries AD the empire flourished and added new territories, notably ancient Britain, Arabia, and Dacia (now Romania). People from the Roman provinces flocked to Rome, where they became soldiers, bureaucrats, senators, and even emperors. Rome developed to become the social, economic and cultural capital of the Mediterranean world. Despite the attention paid to tyrannical and often ferocious leaders such as emperors Caligula and Nero, most emperors ruled sensibly and competently until military and economic disasters led to the political instability of the 3rd century AD. The Empire Roman encompassed a huge amount of territory, but also allowed people of many different cultures to retain their heritage into modern times.