L. Munatius Plancus to Cicero, written from Cularo (modern Grenoble) in the territory of the Allobroges on 6 June 43 BC — Perseus dateline Scr. Cularone in finibus Allobrogum viii Id. Iun. a. 711 (43) and closing subscript in the letter itself. This is the dispatch in which Plancus reports Lepidus’s defection to Antony, the most consequential single piece of news to reach Rome between Mutina in April and the formation of the triumvirate in November.

Lepidus had joined Antony on 29 May. The nominally Senate-loyal commander of Narbonensis and Nearer Spain, with seven legions, had crossed over into open coalition with the man the Senate had declared a public enemy. Plancus, advancing from Transalpina to support Lepidus, learnt of the defection when the joined armies were already on the move against him; his account of the withdrawal — bridges broken on the Isara, not a soldier lost, baggage train intact, the bitterness of the “parricides” that he had slipped through their fingers — is the work of a commander who knows he will be judged on whether he can extract himself in order. The first section is an explicit defence against the charge of temeritas: he had never, he says, really trusted Lepidus; what drove him to advance into contact was pudor — the fear of being charged with feeding the war by his own inaction. The self-portrait is part of the letter’s political work.

The middle of the letter does three further pieces of business. It absolves M. Iuventius Laterensis, the Senate’s man inside Lepidus’s camp, from blame and reports his attempted suicide — a small but politically careful kindness toward the family. It itemises the grievances Lepidus’s troops carried against Plancus (refusing to receive Antony’s envoys; intercepting the tribune Catius Vestinus with Antony’s letter; refusing to negotiate) so that the Senate will know on what side of the war Plancus has been all along. And it calls urgently for reinforcement: Octavian, with his five legions and growing ambition, must be sent up the peninsula, or his army at least dispatched, or the republican cause in Gaul will not hold. The closing personal coda to Cicero — “I hold you dearer every day” — is the conventional intimacy that frames the substance: I have been loyal; I have been prudent; I need you to send the legions north now.