In his Defence of Marcellus (late summer of 46 bc) Cicero had urged the senators he was addressing to be on the alert and protect Caesar from possible conspiracies. And he talked at length about the ‘madness’ of those who would conceive or plan an attempt on Caesar's life, even – he specifies, turning directly to Caesar – ‘among the ranks of your own’. It is strange that he felt the need to point out this possibility to the Senate and, above all, to Caesar himself. ‘Still, since there are in the human mind corners so dark and recesses so unexplored, let us by all means intensify your suspicions; for by so doing we shall intensify your watchfulness.’ These are not idle words: it is a plea that could not have come out of nothing. This may also be inferred from Cicero's indication that the attempt could be hatched ‘de tuis’ or ‘ex eo numero qui una tecum fuerunt’, as well as ‘ex inimicis’.

One is tempted to observe that the insistence with which Cicero stresses that there are no more enemies suggests a wish – surprising though this may be – to signal that some such wild scheme could arise only among the Caesarians. That he has something definite in mind may be deduced from the fact that, after a brilliant demonstration that there could not be any potential conspirators (unless they were completely insane), he nevertheless arrives at the conclusion that the minds of men are such that vigilance must be stepped up!