From the Twelve Tables
“The Law of the Twelve Tables commands that anyone who has conspired with an enemy against the state or handed a citizen to a public enemy, should suffer capital punishment.”
Marcianus, ap. Dig., XLVIII, 4, 3: Lex XII Tabularum iubet eum qui hostem concitaverit quive civem hosti tradiderit capite puniri.
Cicero, De Legibus 3.2
“[Cases concerning] death and citizenship must not be pursued except before the greatest assembly and those whom the censors have recorded in the rolls of the citizens.”
de capite civis nisi per maximum comitiatum ollosque, quos censores in partibus populi locasint, ne ferunto.
The death penalty is not the enactment of justice, it is the execution of vengeance when justice is impossible or not actually desired. It does not function as a deterrent. It is meted out disproportionately to people without financial and social capital, which in the United States means that people of color face capital charges and are executed at far higher rates. The moral peril is compounded by the imperfection of our criminal system where at least 1 in 25 people on death row are actually innocent. The death penalty is not part of a justice system, it is part of a vengeance system.
Note the connection in several passages between the sanctity of the state, the power to end a life, and citizenship.
Xenophon, Apology 25
“These opponents have not said that I am guilty of any of the actions for which the established penalty is death–robbing a temple, theft, enslaving someone, betraying the state…”
ἐφ᾿ οἷς γε μὴν ἔργοις κεῖται θάνατος ἡ ζημία, ἱεροσυλίᾳ, τοιχωρυχίᾳ, ἀνδραποδίσει, πόλεως προδοσίᾳ, οὐδ᾿ αὐτοὶ οἱ ἀντίδικοι τούτων πρᾶξαί τι κατ᾿ ἐμοῦ φασιν.
Plato, Laws 856b-d
“Whoever raises a human being into power and thus enslaves the laws, whoever makes the state subordinate to his petty faction and transgresses what is right by doing all of this violently and stirring up civil strife, he should be considered the most inimical to the whole state.
And the kind of person who does not share these actions, but does occupy some of the most important offices of the state and either fails to observe them or does not fail but will not avenge his country because of cowardice, he should be considered as a citizen at a second degree of evil.
Let each person whose worth is small bear witness to the officers of the state by bringing this person to court for his plotting violent and unconstitutional revolution. Give them the same charges we have for temple robbery and run the trial as it is in those cases where the death penalty comes by majority vote.”
ὃς ἂν ἄγων εἰς ἀρχὴν ἄνθρωπον δουλῶται μὲν τοὺς νόμους, ἑταιρείαις δὲ τὴν πόλιν ὑπήκοον ποιῇ, καὶ βιαίως δὴ πᾶν τοῦτο πράττων καὶ στάσιν ἐγείρων παρανομῇ, τοῦτον δὴ διανοεῖσθαί δεῖ πάντων πολεμιώτατον ὅλῃ τῇ πόλει. τὸν δὲ κοινωνοῦντα μὲν τῶν τοιούτων μηδενί, τῶν μεγίστων δὲ μετέχοντα ἀρχῶν ἐν τῇ πόλει, λεληθότα τε ταῦτα αὐτὸν ἢ μὴ λεληθότα, δειλίᾳ δ᾿ ὑπὲρ Cπατρίδος αὑτοῦ μὴ τιμωρούμενον, δεῖ δεύτερον ἡγεῖσθαι τὸν τοιοῦτον πολίτην κάκῃ. πᾶς δὲ ἀνὴρ οὗ καὶ σμικρὸν ὄφελος ἐνδεικνύτω ταῖς ἀρχαῖς εἰς κρίσιν ἄγων τὸν ἐπιβουλεύοντα βιαίου πολιτείας μεταστάσεως ἅμα καὶ παρανόμου. δικασταὶ δὲ ἔστωσαν τούτοις οἵπερ τοῖς ἱεροσύλοις, καὶ πᾶσαν τὴν κρίσιν ὡσαύτως αὐτοῖς γίγνεσθαι καθάπερ ἐκείνοις, τὴν ψῆφον δὲ θάνατον φέρειν τὴν πλήθει νικῶσαν.
Lycurgus, Against Leocrates, 126-7
“It is right that punishments for other crimes come after them, but punishment for treason should precede the dissolution of the state. If you miss that opportune moment when those men are about to do something treacherous against their state, it is not possible for you to obtain justice from the men who did wrong: for they become stronger than the punishment possible from those who have been wronged.”
τῶν μὲν γὰρ ἄλλων ἀδικημάτων ὑστέρας δεῖ τετάχθαι τὰς τιμωρίας, προδοσίας δὲ καὶ δήμου καταλύσεως προτέρας. εἰ γὰρ προήσεσθε τοῦτον τὸν καιρὸν, ἐν ᾧ μέλλουσιν ἐκεῖνοι κατὰ τῆς πατρίδος φαῦλόν τι πράττειν, οὐκ ἔστιν ὑμῖν μετὰ ταῦτα δίκην παρ’ αὐτῶν ἀδικούντων λαβεῖν· κρείττους γὰρ ἤδη γίγνονται τῆς παρὰ τῶν ἀδικουμένων τιμωρίας.
Plato, Laws 881a-b
“Death is not the most extreme penalty–there are those described in Hades for offenses like this which are beyond death and are truly described, but they are useless in deterring some kinds of minds from their crimes.”
θάνατος μὲν οὖν οὐκ ἔστιν ἔσχατον, οἱ δὲ ἐν Ἅιδου τούτοισι λεγόμενοι πόνοι ἔτι τε τούτου εἰσὶ μᾶλλον ἐν ἐσχάτοις, καὶ ἀληθέστατα λεγόμενοι οὐδὲν ἀνύτουσι ταῖς τοιαύταις ψυχαῖς ἀποτροπῆς·
From Brill’s New Pauly on the death penalty in Greece and Rome by Gottfriend Schiemann:
“In Athens not only premeditated killing (phónos) and sedition and high treason (katálysis toû dḗmoû, prodosía ) resulted in the death penalty, but also religious offences such as desecration of the temple (hierosylía) and (cf. in particular the case against Socrates , 399 BC) publicly taught godlessness (asébeia). In a similar way, in Rome there was provision for the state death penalty for sedition and high treason (perduellio) by beheading (decollatio , in Greece apokephalízein) with an axe, later a sword. In the Roman Imperial period this was the typical death penalty for honestiores , but now sometimes also for homicide.”