Now, with Marcellus dead, Augustus arranged for the marriage of Agrippa to his daughter Julia the Elder, who was previously the wife of Marcellus. Agrippa was given "tribunicia potestas" ("the tribunician power") in 18 BC, a power that only the emperor and his immediate heir could hope to attain. The tribunician power allowed him to control the Senate, and it was first given to Julius Caesar. Agrippa acted as tribune in the Senate to pass important legislation and, though he lacked some of the emperor's power and authority, he was approaching the position of co-regent.