where was the roman empire centered?
Rome
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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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 By the end of this period , Rome had effectively completed the conquest of their immediate Etruscan and Latin neighbours , and also secured their position against the immediate threat posed by the nearby Apennine hill tribes . 

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 The Roman army succeeded in conquering many territories covering the entire Mediterranean region and coastal regions in southwestern Europe and north Africa . These territories were home to many different cultural groups , both urban populations and rural populations . Generally speaking , the eastern Mediterranean provinces were more urbanised than the western , having previously been united under the Macedonian Empire and Hellenised by the influence of Greek culture . 

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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 . 
