The originality of Polybius’ theory depended on his conception about the power relations of politics behind the scene. His claim for a mixed constitution, foresaw a check and balance system for the conflicting powers. According to him, the success of Roman constitution was to ensure this check and balance system. Polybius built his constitutional understanding on not the social classes but? political forces? and institutional? balance. It can be?said that he pointed? out the way for the ?modern constitutional? separation of powers? system.