The Lex Trebonia was passed in 55 BC during the second joint consulship of Marcus Licinius Crassus and Gnaeus Pompeius Magnus ("Pompey the Great"). Sponsored by the tribune Trebonius, the legislation granted each outgoing consul an extended five-year proconsular command. Crassus received the province of Syria, with the barely disguised intention of launching an invasion of Parthia. Pompeius received the provinces of Nearer Spain and Further Spain, but remained in Rome and conducted his administration through legates.
At the same time, Gaius Julius Caesar's term as governor of the provinces Transalpine Gaul, Cisalpine Gaul and Illyricum was extended, hostilities in Gaul having reignited. By law, Caesar could not run for a second consulship until 10 years after his first, and he wished not to return to Rome as a private citizen.