Claims that Roman Empire's population was 60mln people is a claim by biased Europocentrist historians from Europe.....European estimates of Roman Empire's population range between 30mln and 60mln people with 30mln being closer to reality.
From military point of view Romans were no match even for Persian Empire.....If you analyze history of Roman-Persian wars you will see that Persia was a superior military power
Here is a brief analysis of Roman-Persian wars:
Roman-Parthian War 53BC-------Crassus invades Parthia----Parthian victory (Crassus and his son Publius killed, Parthians raid Syria)
Roman-Parthian war 40bc-38BC------Parthians invade Syria and Palestine and Asia Minor but forced to withdraw------Roman victory (Prince Pacorus killed)
Roman-Parthian war 36bc-20bc------Mark Anthony invades Armenia------Parthian victory (32.000 Romans killed)
Roman–Parthian War of 58–63------Parthians install their man in Armenia----Stalemate (Arsacid will rule Armenia but he will be a nominal Roman client)
Roman-Parthian war 115-117-----Trajan invades Parthia, takes Armenia and Mesopotamia including capital Ctesiphon, but forced to withdraw due to rebellions in Mesopotamia and Palestine and Parthian attacks, Hadrian restores status quo---Stalemate
Roman–Parthian War of 161–166---Vologases invades Armenia and Syria defeating their governors and plundering the land--Romans expel Parthians from Syria and invade Mesopotamia taking and looting Ctesiphon--Romans forced to withdraw due to epidemy---Roman victory
Roman-Parthian War 195–197----Septimus Severus invades Parthia annexes Northern Mesopotamia and sackes Ctesiphon---Roman Victory
Roman-Parthian War 210-217----civil war in Parthia---Caracalla takes advantage and invades Parthia and plunders Mesopotamia---after Caracallas assasination battle of Nisibis won by Parthians---Parthian victory (Rome withdraws and pays compensation for destruction made by Caracalla)
Roman-Sassanid War 230-244------Ardasher and Shapur invade Syria and Mesopotamia (taking Carrhae, Nisibis, Hatra)-Carrhae and Nisibis retaken by the Romans---Emperor Gordian III killed and Romans defeated at Misiche and pay compensation---Sassanid Victory
Roman-Sassanid War 250-260----Shapur I invades Armenia and Syria (plunderes Antioch) defeats Romans in Battle of Barbalissos and Battle of Edessa---Roman Emperor Valerian captured in Edessa, ---Shapur moves to Anatolia but defeated there and forced to withdraw from Syria and Armenia---Stalemate
Roman-Sassanid War 283-----Sassanids are busy in Afghanistan and have internal problems---Carus captures Ctesiphon---Roman Victory
Roman-Sassanid War 297-298----Narseh invaded Armenia and defeates Romans, but Galerius defeats Narseh, sackes Ctesiphon and captures royal harem---Roman Victory
Roman-Sassanid War 335-363---Shapur invades and takes cities in Syria, but Romans retake them---Emperor Julian killed in the Battle of Samarra--elected Emperor Jovian makes major concessions in return for peace and safe passage----Sassanid Victory
Roman–Sasanian War of 421–422---Rome declares war in response to persecution of Christians----Stalemate
Roman–Sasanian War of 440 ---Rome pays tribute to Persia-----Sassanid Victory
TOTAL RESULT:
15 Wars between 53BC-440AD---493 years of war---1 war every 33 years on average
6 Persian victories vs 5 Roman victories and 4 Stalemates
Persia kills Triumvirate member Crassus and his son Publius and captures Roman Standards, kills Roman Emperor Julian (and possibly Gordian III) and captures and humiliates Emperor Valerian
Rome kills Prince Pacorus (son of Shah Orodes II), captures Narseh's royal harem and captures Ctesiphon 5 times (city on the border)
Rome is aggressive 6 times
Persia is aggressive---6 times
+3 wars because of provocations and actions of the other side
Rome raids Mesopotamia 5 times
Persia raids Syria/Asia Minor/Palestine---5 times
Byzantine-Sassanid War 502-506----Kavad I demands money, Anastacius says no---Kavad invades and takes cities but pushed back----Peace treaty with Persians not holding any territory and Byzantines paying tribute-----Sassanid Victory
Byzantine-Sassanid War 526-532----Iberia (in Georgia) defected to Byzantine because Persians wanted to convert them to Zoroastrianism----no territorial changes, Justinianian Byzantine pays a tribute to Khosrau I-----Sassanid Victory
Byzantine-Sassanid War 541–562-----Justinian conquers territory of the former Western Empire and Khosrau I attacks---Khosrau plunders Syria and deports Antioch population to Persia and invades Lazica---multiple battles and Persian victories--Rome pays annual tribute----Sassanid victory
Byzantine–Sassanid War 572–591-----Armenia and Iberia had pro-Byzantine rebellions against Persia which Rome supported---Khosrau invades Syria and Anatolia but forced to withdraw to Mesopotamia---Romans invade Mesopotamia---battles are inconclusive---Khosrau dies and Hormizd continues war---Bahram Chobin rebells against Hormizd---Hormizd dismissed and Khosrau II put in power----Khosrau asks Romans for help and after defeating Bahram becomes shah and gives land to Romans-----Roman Victory
Byzantine–Sasanian War of 602–628-----Khosrau II attacks and occupies Syria, Palestine, Egypt, Anatolia and lay siege to Constantinople----Roman empire nearly collapsed---counterattack by Heraclius restores status quo--True Cross returned--Stalemate
TOTAL RESULT:
20 wars between 53BC-628AD-----681 years of war---1 war every 34 years on average
9 Persian victories vs 6 Roman victories and 5 Stalemates
Persia kills Triumvirate member Crassus and his son Publius and captures Roman Standards, kills Roman Emperor Julian (and possibly Gordian III), Captures and humiliates Emperor Valerian and captures the True Cross
Rome kills Prince Pacorus (son of Shah Orodes II), captures Narseh's royal harem and captures Ctesiphon 5 times (city on the border)
Rome is aggressive 6 times
Persia is aggressive---9 times
+5 wars because of provocations and actions of other side
Rome raids Mesopotamia 7 times
Persia raids Syria/Asia Minor/Palestine---8 times