Ancient Rome - Most Important Event?

the single most important event? I'd say it was something not even on the list, the destruction of the Republic, as that is what eventually led to the undermining of Roman power and the fall of the Empire. Of the factors on the list, I'd say it was the establishment of the Republic in 509 BCE - the Republic, although the Romans hardly realised it, was the strongest institution the Romans had. Destroying it led to civil war on an epic scale and an increasingly corrupt and inefficient line of emperors and tyros.