What were three forms of government did Ancient Rome have between about600b.c. And 44b.c.?

Between 600 BC and 44 BC Rome had two forms of government, not three: a monarchy (which lasted 244 years, form 753 BC to 509 BC and a republic, which lasted from 509 BC to 27 BC. The assassination of Julius Caesar in 44 BC did not mark the end of the republic. In fact his assassination was meant to save the republic. This form of government lasted until Octavian won the final civil war of the Republic in 30 BC and its end was formalised in 27 BC. The third form of government was rule by emperors, which lasted from 27 BC to 476 AD.