Cicero to C. Cassius Longinus, written from Rome before the kalends of January 709 AUC — month-precision January 45 BC, the Perseus dateline giving only ante m.\ Ian. The first of the three letters in this cluster in which Cicero engages Cassius on his recent conversion to Epicureanism. The joke runs through the opening: Cicero, writing to a silent correspondent, imagines Cassius vividly present as he writes — and disclaims that this presence arrives by Democritean [Greek: eidōla], the atomic images of the school, here teased through the Latin coinage spectra of Catius the Insubrian, the recently dead Epicurean popularizer.

The second section presses the joke philosophically: even if the eye could be struck by spectra, the mind cannot. Cicero asks whether Cassius’s spectrum is at his command, and whether the island of Britain — a place neither has seen but both can think of — will send him its [Greek: eidōlon] at will. The third turns into the running gag of the diptych: a mock-interdict demanding Cassius’s restoration to the school [Greek: hairesei] from which the men under arms (Caesar’s victory) have ejected him, written in the language of the praetor’s interdict “vi hominibus armatis.” The letter ends in the period’s standard guarded coda: he writes about philosophy because the state cannot be written about.