To compensate for this risk, he had his tribunician powers (potestas tribunicia) modified. The Tribunate was a natural fit for an autocrat who sought to maintain popularity with the people. The Tribunate was a popular office, because it had been the principal vehicle through which plebeians gained political power and through which they had been protected against the abuses of the state. The "Plebeian Tribunes" had strong positive powers, such as the right to convene the Plebeian Council, and strong negative powers, such as the right to veto an act of the senate. In addition, by history and precedent, the Tribunate, unlike the Consulship, was radical by nature. Augustus' modifications didn't change the actual powers associated with the office, but instead, Augustus simply displayed his tribunician status more vividly. While he had held tribunician powers since 36 BC, these powers were never renewed. After 23 BC, however, he had these powers renewed every year. In official documents, he indicated the number of years that had elapsed since he first held tribunician power. After these reforms had been instituted, Augustus never again altered his constitution. At various points, the people demanded that he take more powers, but he refused. In a few instances, he had to exercise powers that he did not legally have, but he usually acquired these powers by securing the passage of temporary legislation. Augustus' final goal was to figure out a method to ensure an orderly succession. Under Augustus' constitution, the Senate and the People of Rome held the supreme power, and all of his special powers were granted for either a fixed term, or for life. Therefore, Augustus could not transfer his powers to a successor upon his death. Any successor needed to have powers that were independent of Augustus' own powers. During his illness in 23 BC, he had chosen Agrippa to be his successor. He had considered the possibility of making his nephew Marcellus his successor, but had ultimately decided that Marcellus was too young. In 21 BC Marcellus died and Augustus married Agrippa to his daughter Julia, and in 18 BC Augustus enacted a law that granted Agrippa tribunician powers for a period of five years. Agrippa and Julia had two sons, Gaius and Lucius Caesar, and Augustus designated them as possible heirs by granting upon both tribunician powers. In 12 BC Agrippa died, and in 6 BC Augustus granted these tribunician powers