what does the roman empire consist of?
Cilicia
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 The Roman Empire was among the most powerful economic , cultural , political and military forces in the world of its time . It was the largest empire of the ancient history era , and one of the largest empires in world history . At its height under Trajan , it covered 5 million square kilometers , a territory composed of 48 nations in the 21st century . It held sway over an estimated 70 million people , at that time 21 % of the world 's entire population . The longevity and vast extent of the empire ensured the lasting influence of Latin and Greek language , culture , religion , inventions , architecture , philosophy , law and forms of government on the empire 's descendants . Throughout the European medieval period , attempts were even made to establish successors to the Roman Empire , including the Empire of Romania , a Crusader state , and the Holy Roman Empire . By means of European colonialism following the Renaissance , and their descendant states , Greco @-@ Roman culture was exported on a worldwide scale , playing a crucial role in the development of the modern world . 

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 The Roman Empire ( Latin : Imperium Rōmānum ; Classical Latin : [ ɪmˈpɛ.ri.ũː roːˈmaː.nũː ] Koine and Medieval Greek : Βασιλεία τῶν Ῥωμαίων , tr . Basileia tōn Rhōmaiōn ) was the post @-@ Roman Republic period of the ancient Roman civilization , characterized by government headed by emperors and large territorial holdings around the Mediterranean Sea in Europe , Africa and Asia . The city of Rome was the largest city in the world c . 100 BC – c . 400 AD , with Constantinople ( New Rome ) becoming the largest around 500 AD , and the Empire 's populace grew to an estimated 50 to 90 million inhabitants ( roughly 20 % of the world 's population at the time ) . The 500 @-@ year @-@ old republic which preceded it was severely destabilized in a series of civil wars and political conflict , during which Julius Caesar was appointed as perpetual dictator and then assassinated in 44 BC . Civil wars and executions continued , culminating in the victory of Octavian , Caesar 's adopted son , over Mark Antony and Cleopatra at the Battle of Actium in 31 BC and the annexation of Egypt . Octavian 's power was then unassailable and in 27 BC the Roman Senate formally granted him overarching power and the new title Augustus , effectively marking the end of the Roman Republic . 

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 The Empire reached its largest expanse under Trajan ( reigned 98 – 117 ) , encompassing an area of 5 million square kilometers that as of 2009 was divided among forty different modern countries . The traditional population estimate of 55 – 60 million inhabitants accounted for between one @-@ sixth and one @-@ fourth of the world 's total population and made it the largest population of any unified political entity in the West until the mid @-@ 19th century . Recent demographic studies have argued for a population peak ranging from 70 million to more than 100 million . Each of the three largest cities in the Empire — Rome , Alexandria , and Antioch — was almost twice the size of any European city at the beginning of the 17th century . 

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 The Roman Empire was one of the largest in history , with contiguous territories throughout Europe , North Africa , and the Middle East . The Latin phrase imperium sine fine ( " empire without end " ) expressed the ideology that neither time nor space limited the Empire . In Vergil 's epic poem the Aeneid , limitless empire is said to be granted to the Romans by their supreme deity Jupiter . This claim of universal dominion was renewed and perpetuated when the Empire came under Christian rule in the 4th century . 

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 During the first two centuries of its existence , the Roman Republic expanded through a combination of conquest and alliance , from central Italy to the entire Italian peninsula . By the following century , it included North Africa , Spain , and what is now southern France . Two centuries after that , towards the end of the 1st century BC , it included the rest of modern France , Greece , and much of the eastern Mediterranean . By this time , internal tensions led to a series of civil wars , culminating with the assassination of Julius Caesar , which led to the transition from republic to empire . The exact date of transition can be a matter of interpretation . Historians have variously proposed Julius Caesar 's crossing of the Rubicon River in 49 BC , Caesar 's appointment as dictator for life in 44 BC , and the defeat of Mark Antony and Cleopatra at the Battle of Actium in 31 BC . However , most use the same date as did the ancient Romans themselves , the Roman Senate 's grant of extraordinary powers to Octavian and his adopting the title Augustus in 27 BC , as the defining event ending the Republic . 
