The history of Roman Law can be divided into three systems of procedure: that of "legis actiones", the "formulary system", and "cognitio extra ordinem". The periods in which these systems were in use overlapped one another and did not have definitive breaks, but it can be stated that the legis actio system prevailed from the time of the XII Tables (c. 450 BC) until about the end of the 2nd century BC, that the formulary procedure was primarily used from the last century of the Republic until the end of the classical period (c. AD 200), and that of cognitio extra ordinem was in use in post-classical times. Again, these dates are meant as a tool to help understand the types of procedure in use, not as a rigid boundary where one system stopped and another began.