What type of government did the ancient Romans create?

ancient Rome passed through three general forms of government during its long existence- monarchy, republic, and empire.

1. It began as a kingdom, and legend places its founding in 753 BC. The kingship lasted for seven generations of kings, though there appears to have always been some resemblance of a Senate- a group of wealthy aristocrats called "patricians" who would meet to better organize their interests. The last king, Tarquinius Superbus, was expelled by a patrician uprising led by Brutus around 510 BC.

2. Brutus established the consulship, where patricians elected two leaders to govern Rome. Brutus executed his own sons, who coveted the "throne" and a return to monarchy, to demonstrate that the consular positions would not be hereditary. The plebians (i.e., the non-slave population not considered to be members of this Senatorial patrician class) succeeded early in the 5th century in establishing a tribune that would hold veto power over decisions of the Senate. It was under this Republican government that Rome really expanded to control much of the land that would become its empire. Eventually, as Rome's territory increased, the military and military commanders began to hold more sway. The general Sulla pronounced himself a dictator in 86 BC, and when he died, two long civil wars destroyed what remained of the republican system.

3. In 27 BC, the Senate made Octavian Augustus Caesar the first Emperor (Imperator) of Rome. Although there were many attempts to make the position a hereditary one, military commanders, and especially the Emperor's special security force- the Praetorian Guard- had the most influence over who ruled the Empire. The imperial form of government lasted in the West until 476 AD, when Odoacer forced the last emperor, Romulus Augustus, to abdicate. The Empire survived in Constantinople until it was conquered in 1453 by Sultan Mehmed II and the Ottoman Turks.