Cicero to M. Licinius Crassus, son of Publius, written from Rome in January 54 BC. The recipient is the triumvir himself, second consul of 70 and 55 BC, by this date already en route to his Syrian command for the Parthian campaign that would end fifteen months later in his death at Carrhae (May 53 BC). The letter is not the routine recommendation of Fam. 5.5 (62 BC), but the formal repair of a political relationship: the public profession of an alliance that has, until now, been at best uneven.

The chain of recent events is there in the §1 phrase “perpetual championship of all your honours.” Crassus’s consulship of 55 BC — the second consulship of the Luca compact, which Cicero had returned from his Antium retreat to support after Luca — had been followed by the senatorial debates over the Syrian command and its prerogatives, in which Cicero (against the consuls of 54, Ap. Claudius and L. Domitius Ahenobarbus, the latter Crassus’s bitter enemy) defended Crassus’s settlement. The letter records, after the fact, the change of side that the post-Luca compact had required. The candour of the §2 admission —“certain plagues of men, those who grieve at another’s praise, sometimes turned you against me and sometimes changed me towards you” — is the only direct acknowledgement Cicero ever wrote to Crassus of the years of mutual coolness.

The structural turn at §4–5 is to the two Crassi — M. Crassus the elder son (the future consul of 30 BC) and the famously brilliant younger son P. Crassus, who had served in Caesar’s Gallic command and would die in the Parthian campaign with his father. Cicero’s particular bond is with Publius (§4: “observes and loves me as a second parent” — the line on which much of Cicero’s literary judgement of the boy as the heir-apparent of republican ingenium has rested). Tertulla, Crassus’s wife, and the boys are the connecting persons; the political alliance is mediated through them.

The closing note — “this letter has the force of a treaty, not of a letter” — is the formal commitment, by Cicero, to act as Crassus’s standing agent in absentia, on all matters public, private, forensic, domestic, of friends, guests, and clients. The letter would in fact prove the sincere foundation of Cicero’s late friendship with the younger Crassus and, after Carrhae, of his careful working relations with the family. With Crassus dead at Carrhae and the triumvirate broken, the alliance Cicero pledged here would turn within five years into the political balance that he would in turn lose: when Caesar crossed the Rubicon (January 49 BC), the senate had no third triumvir to lean on.