"taking the form of a slave"

Grünewald

"The ignominy of a public trial is a miserable thing,—the deprivation of a man's property by way of penalty is a miserable thing,—exile is a miserable thing; but still, in all these disasters some trace of liberty remains to one. Even if death be threatened, we may die free men; but the executioner, and the veiling of the head, and the mere name of the [cross (crucis)], should be far removed, not only from the persons of Roman citizens—from their thoughts, and eyes, and ears. For not only the actual fact and endurance of all these things, but the bare possibility of being exposed to them,—the expectation, the mere mention of them even,—is unworthy of a Roman citizen and of a free man. Does not the kindness of their masters at one touch deliver our slaves from the fear of all these punishments; and shall neither our exploits, nor the purity of our past life, nor the honours which you have conferred on us, save us from the scourge, from the hangman's hook, and even from the dread of the [cross (crucis)]?"

     Cicero, Pro C. Rubirio oratio 5.16, trans. C. D. Yonge, who used for "crux" "gibbet," not "cross."  A passage cited (whether accurately or not) as proof of the claim that "Crucifixion was not only the most agonizing [(atroce)] of punishments/tortures, 'summum supplicium' (Digest, De poenis 48.19.28), it was also the most degrading, that of slaves, 'servile supplicium' (Tacitus, Historiae 4.11), and that of great criminals; normally one did not crucify a Roman citizen (Cicero, Contra Verrem 2.5.64 (165), 66).  The cross, 'arbor infelix' (Livy, Historia 1.26.6; Cicero, Pro C. Rubirio oratio 4.13), was synonymous with horror and abjection" (Dictionnaire de spiritualité, sv Folie de la croix I, by Donatien Mollat, vol. 5 (1964), col. 639).  Latin from here.