TheLex Trebonia was aRoman law passed in 55 BC during the second jointconsulship ofMarcus Licinius Crassus andPompey, as part of their informal political arrangement known as theFirst Triumvirate. Sponsored by thetribune of the plebsGaius Trebonius, the legislation granted each outgoing consul an extended five-yearproconsular command, similar to the one granted toJulius Caesar for hisconquest of Gaul. Crassus received theprovince ofSyria, with the barely disguised intention oflaunching an invasion ofParthia. Pompey received the provinces ofHispania Citerior andHispania Ulterior, but remained in Rome and conducted his administration throughlegates.
At the same time,Gaius Julius Caesar's term asgovernor of the provincesTransalpine Gaul,Cisalpine Gaul andIllyricum was extended, hostilities in Gaul having reignited. By law, Caesar could not run for a second consulship until ten years after his first, and he wished not to return to Rome as aprivate citizen.