The Constitution of the Roman Empire was an unwritten set of guidelines and principles passed down mainly through precedent. After the fall of the Roman Republic, the constitutional balance of power shifted from the Roman Senate to the Roman Emperor. Beginning with the first emperor, Augustus, the emperor and the Senate were theoretically two co-equal branches of government. In practice, however, the actual authority of the imperial Senate was negligible, as the emperor held the true power of the state. During the reign of the second emperor, Tiberius, many of the powers that had been held by the Roman assemblies were transferred to the Senate.