The cosmos is a polis (πόλις) — an ordered civic community — and the gods, together with rational human beings, are its co-citizens (συμπολῖται). What binds them is the common Logos (reason), which functions in this polis as law (νόμος): what the nature of the whole obeys is at the same time the moral law for rational beings. Membership in this cosmopolis is prior to any particular ethnic or political affiliation: as Antoninus, I am a citizen of Rome; as a human being, a citizen of the cosmos (Med. 6.44; 10.15; 12.36).

The cosmopolis has several distinguishing marks:

• Universality. Citizenship is not tied to birth, ethnicity, or status — it belongs automatically to everyone who possesses reason. It includes gods, Greeks, barbarians, men, women, slaves, and the free.
• Antiquity. Marcus calls it πρεσβυτάτη πόλις — "the most ancient polis": it was not founded, like Athens or Rome, but has existed always along with the cosmos.
• Constitution = Logos. The law of the cosmopolis is not the law of a particular people but the rational order of the cosmos itself. Hence "to be a citizen" = "to live according to the Logos" = to live according to nature.
• Social ethics. From shared citizenship follow concrete duties toward fellow-citizens: justice (dikaiosyne), natural affection (philostorgia), and an unperturbed attitude in TERMkinship.

The Cynic predecessor: Diogenes of Sinope — DL VI 63: to the question "where are you from?" he answered «κοσμοπολίτης εἰμί» ("I am a citizen of the cosmos"). This famous coinage is the first in ancient literature.

Zeno the Stoic (SVF I 262) — in his Politeia he develops the doctrine of a universal polis; the fragment reports: "he held that we should not live by cities and nations, marked off from one another by their separate justices, but should regard all human beings as fellow-citizens and fellow-tribesmen — and that there should be one order and constitution of life, as with a herd grazing together under a common law." Zeno's Politeia was radical (Plutarch, De Alex. fort. I 6, calls it a "utopia"): without money, without temples, without law-courts, without separate marriages.

Chrysippus and the Middle Stoa — SVF III 333–348: a moderate reading. The cosmopolis does not abolish particular cities but surpasses them as a higher order.

Cicero — De legibus I 22–23: "universus hic mundus una civitas communis deorum atque hominum existimanda [est]" ("this whole universe must be regarded as one city common to gods and human beings"); in the same place, shared reason is the law that binds gods and humans into a single commonwealth. Through Cicero the conception enters Roman public law.

Seneca — De otio IV 1: "duas res publicas animo complectamur, alteram magnam et vere publicam... alteram cui nos adscripsit condicio nascendi" ("we embrace two commonwealths in our mind — the great and truly common one … and the one to which the condition of birth has assigned us"). Ep. 28.4; 68.

Marcus — Med. 2.16; 3.11; 4.4 (the sorites-proof: common νοῦς → common λόγος → common law → we are citizens → «ὁ κόσμος ὡσανεὶ πόλις» — "the cosmos is in a manner a state"; see 04-04); 05-22 (the civic criterion of harm: the citizen suffers no harm unless the city does); 05-30; 05-35; 06-14 (the summit of the value-hierarchy — the rational, universal, and political soul, καθολικὴ καὶ πολιτική); 06-44 (the most celebrated place: «ὡς Ἀντωνίνῳ μοι ἡ πόλις καὶ ἡ πατρὶς Ῥώμη, ὡς δὲ ἀνθρώπῳ ὁ κόσμος» — "as Antoninus, my city and fatherland is Rome; as a human being, the cosmos"); 07-09 (νόμος εἷς — one law, one common λόγος of all thinking beings); 07-13 (μέλος τοῦ ἐκ τῶν λογικῶν συστήματος — a member of the system of rational beings); 07-53 (the κοινὸς θεοῖς καὶ ἀνθρώποις λόγος — the common citizenship of reason); 08-02 (the present work — of a being ἰσόνομον θεῷ, sharing one law with god); 08-54 (συμφρονεῖν τῷ περιέχοντι πάντα νοερῷ — to think-with the common intelligence); 09-23 (you are a completing part of the πολιτικὸν σύστημα; let every act complete the ζωὴ πολιτική); 10.15; 12.36.

In 02-16 the cosmopolis appears in the final formulation of the τέλος of rational beings: "to follow the reason and law of πρεσβυτάτη πόλις καὶ πολιτεία" — the most ancient city and its constitution. It matters that this is the closing argument of the fifth point (concerning aimless actions): even a small action must be aligned with a τέλος, and the τέλος of rational beings is participation in the cosmopolis. So for Marcus cosmopolitanism is not a rhetorical declaration ("citizen of the world") but an operational ethical criterion: every action that does not fit into the order of the cosmopolis is an action without a σκοπός — and so a violation of one's own rational nature.

Distinction from unity-of-cosmos: unity-of-cosmos is the ontological doctrine (the cosmos as a single whole, with the parts in sympathy across the pneumatic continuum); cosmopolis is the political-ethical articulation of the same reality (the cosmos as a polis of rational beings). One is about connection, the other about citizenship.

Historical legacy. The Stoic cosmopolis is one of the most influential ancient concepts in Western thought:

• In Roman law through Cicero: the idea of a universal natural law (ius naturale) as a norm above national institutions.
• In early Christianity: the universal human nature ("there is neither Greek nor Jew"; Gal. 3:28) rests, openly or tacitly, on Stoic cosmopolitanism.
• In the Enlightenment: Kant's Zum ewigen Frieden (1795), with its "Weltbürgerrecht," is a direct heir of the Stoic conception; the concept of human rights underlying the UN is its distant descendant.
• In contemporary political philosophy: Martha Nussbaum, The Therapy of Desire (1994) and Cultivating Humanity (1997), openly returns to Stoic cosmopolitanism as an alternative to nationalist political models.