Nah its all good. Roman history is a confusing cluster-fuck of shizz anyway - but yeah the period with Julius Caesar is cool, from Roman Republic to Roman Empire... good times. (Also another little fact - the Colosseum actually only started construction in 70AD under Vespasian, so in a few months from where we are - but again its much more fun with the Colosseum already built).
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 now 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.
The imperial successor to the Republic endured for some 500 years. The first two centuries of the Empire's existence were a period of unprecedented political stability and prosperity known as the Pax Romana, or "Roman Peace". Following Octavian's victory, the size of the Empire was dramatically increased. After the assassination of Caligula in 41, the Senate briefly considered restoring the republic, but the Praetorian Guard proclaimed Claudius Emperor instead. Under Claudius, the Empire underwent its first major expansion since Augustus.
After Claudius' successor, Nero, committed suicide in 68, the Empire suffered a period of brief civil wars, as well as a concurrent major rebellion in Judea, during which four different legionary generals were proclaimed Emperor. Vespasian emerged triumphant in 69, establishing the Flavian dynasty, before being succeeded by his son Titus, who opened the Colosseum shortly after the eruption of Mt. Vesuvius. His short reign was followed by the long reign of his brother Domitian, who was eventually assassinated. The Senate then appointed the first of the Five Good Emperors. The Empire reached its greatest extent under Trajan, the second in this line.
After the fifth Emperor in that line it was Commodus (the guy who is the bad guy in that film Gladiator), he was pretty much a stupid wanna be Hercules, and he messed up the empire big time, which started a decline that eventually ended with the assassination of Alexander Severus in 235, which led to the Crisis of the Third Century in which 26 men were declared Emperor by the Roman Senate over a fifty year period. It was not until the reign of Diocletian that the Empire was successfully stabilized with the introduction of the Tetrarchy, which saw four Emperors rule the Empire at once. The division was ultimately unsuccessful, leading to a civil war that was finally ended by Constantine I, who defeated his rivals and became the sole ruler of east and west. Constantine subsequently shifted the capital of the east to Byzantium, which was renamed Constantinople in his honour.