“Common Peace” is the English term used to describe a series of multilateral treaties contracted between various Greek powers, often also with the involvement of the Persian King, in the 4th century bce. It translates the phrase koinē eirēnē, which is used by Diodorus Siculus (but not by earlier historians) to refer to these agreements.

The precise terms of the various agreements differ, but they share some distinctive qualities. The agreements were multilateral, but although they were nominally universal (“common”), in practice not all Greek states participated in the agreements or were given equal protection by their terms. Their most consistent and significant feature is a guarantee of autonomia (limited independence; see autonomy) to many (but not all) Greek states. Participants in the agreement are expected to take action, including military action, against any breaches of its terms; in earlier agreements this expectation is expressed as a voluntary option, but from the second Common Peace of 371, it appears to have become compulsory. These actions and the Peace more generally are controlled and guaranteed by a major regional power. The Common Peaces are, therefore, inherently hierarchical in their structure.

The first, unsuccessful, attempt to conclude a Common Peace came in 392 (Xen. Hell. 4.8.14–15); a successful attempt followed in 387/6 (Xen. Hell. 5.1.31). Both were brokered by the Spartan Antalcidas, who led negotiations with the Persian king Artaxerxes (2) II (the peace of 387/6 is, therefore, sometimes referred to as the “Peace of Antalcidas” or “King’s Peace“). The 387/6 agreement ceded to the Persian king control over Greek cities in Asia Minor and Cyprus, and left Athens in control of the islands of Lemnos, Imbros, and Scyros. Other Greek cities were declared to be autonomoi, and signatories to the peace undertook to defend this independence; the Persian king, as guarantor of the peace, was given responsibility for ensuring that this happened. In practice, however, it was the Spartans who initially took the lead in enforcing the agreement (or their interpretation of it). In 378/7, however, the Second Athenian Confederacy invoked the terms of the Common Peace in its attempt to establish Athens as the leader of a new, multilateral alliance, singling out the Spartans as a threat to the freedom and autonomy of the Greeks (RO 22, lines 9–15).

The Common Peace was renewed in 375 (Xen. Hell. 6.2.1; Diod. Sic. 15.38) on the initiative of the Persian king Artaxerxes II. The precise terms of this agreement are unclear, but the guarantee of autonomia was certainly included; it seems likely that the agreement also included a new clause which prohibited the presence of foreign garrisons in Greek cities (Diod. Sic. 15.38.2). This peace collapsed within about eighteen months, primarily as a result of tensions between Athens and Sparta. In 371, Sparta attempted to institute another Common Peace (Xen. Hell. 6.3.18). The attempt quickly foundered as a result of disagreements over the interpretation of the autonomia clause, especially as applied to the cities of the Theban-led Boeotian Federation (see Boeotia and Boeotian Confederacy). A second attempt in the same year, instigated by Athens (Xen. Hell. 6.5.1), was more successful, at least in that many Greek city-states were willing to sign up to it. One significant exception, however, was the increasingly powerful city of Thebes. When Thebes invaded the Peloponnese in 370, Athens offered assistance to Sparta; in doing so, the Athenians were (according to Xenophon) especially motivated by the clause in the Common Peace which required them to support signatories who came under attack (Xen. Hell. 6.5.36). In that respect, then, the peace might be argued to have served its purpose. But if the wider intention of the Common Peace was to achieve stability in mainland Greece, it is manifestly clear that it had failed to do so.

Attempts were made to re-establish a multilateral peace in 369 (when the initiative was taken by the Persians: Xen Hell. 7.1.27) and 367/6 (led by the Thebans: Xen. Hell. 7.1.33-40). Neither attempt was successful, and the detailed terms of the proposed agreements are not recorded, but it seems plausible that a Common Peace was the desired outcome in both cases (Diod. Sic. 15.70.2 describes the former as a koinē eirēnē). In 366/5, a peace was successfully concluded. This agreement is described by Diodorus as a Common Peace (15.76.3), but this account is not obviously compatible with that of Xenophon (Hell. 7.4.2–11), which instead characterizes the 366/5 peace as a more restricted agreement between Thebes and Corinth (together with some other Peloponnesian cities). Diodorus (15.89.1) reports that another Common Peace was concluded after the battle of Mantinea in 362, in which all Greek states except Sparta participated. Again, there is no trace of this agreement in Xenophon (who chooses instead to conclude his Hellenica by emphasizing the chaos of the Greek world after Mantinea: Hell. 7.5.27); but references to the agreement in other literary sources (Polyb. 4.33.8–9; Plut. Ages. 35.3­4), as well as in an inscription probably to be dated to 362/1 (IG IV 556 = RO 42), suggest that Diodorus’s account can be trusted.

The peace of 362/1 is the last agreement to which the label “Common Peace” can straightforwardly be applied. But some key elements of these agreements persist in the diplomacy of the later Classical period, and beyond. Some have seen elements of Common Peace rhetoric in the “Peace of Philocrates” of 346. It is less disputed that the League of Corinth (see Corinth, League of), the settlement imposed on Greek cities by Philip (1) II, king of Macedon (and renewed by Alexander (3) the Great), drew heavily on the framework and ideology of the Common Peaces, particularly the promises of autonomia to participating states (RO 76; cf. [Dem.] 17.30). Indeed, the Common Peaces can be seen to play a critical role in embedding the language of freedom and autonomy in Greek interstate rhetoric; this language persists down into the Hellenistic and Roman periods.

Other than this diplomatic legacy, what is the significance of the Common Peaces? It is clear that they did not prevent the regular outbreak of war between Greek states. In fact, it might be argued that they provoked wars by providing powerful states with a mechanism and/or motivation to justify attacks on their rivals. Two characteristics of the Common Peaces were critical in this. First, the flexibility of the concept of “autonomy” could be (and was) exploited by powerful states, who could appeal to a perceived violation of autonomia either to break up potentially threatening federations of smaller states (a tactic pursed especially by the Spartans) or to justify action against their rivals, if they could be argued to be suppressing another state’s autonomia in some way. Secondly, the hierarchical nature of the Common Peaces meant that states who acted as guarantors of the agreements could use this position to consolidate and enhance their status in the Greek world; conversely, their rivals might seek to undermine a Common Peace in order to undermine the position of its guarantor. The fact that a Common Peace was not only compatible with hegemonic power but could even be used to bolster it is already implicit in the formation of the Second Athenian Confederacy and becomes impossible to miss in the adoption of the Common Peace as an instrument of Macedonian imperialism after 337 bce. Overall, then, there are good grounds for characterizing the Common Peaces as nothing more than a tool of power politics, exploited by the four major players in 4th-century interstate politics (Athens, Sparta, Thebes, and Macedon) for their own purposes. The Persian king’s intermittent involvement in the Common Peaces could also be understood as being driven primarily by self-interest: the agreements secured Persian control over their possessions in Asia Minor, temporarily reduced instability on the Persian Empire’s western border, and might also have increased the availability of Greek mercenaries for service in the Persian army (a motivation attributed to Artaxerxes (2) II in the context of the peace of 375, e.g., by Diod. Sic. 15.38.1).

A more optimistic view is also possible. It might be argued that, although the Common Peaces did not prevent either war or empire, they did offer meaningful protections for at least some Greek states. Certainly, the praise of the Common Peace set out in RO 42 (where it is said that the Peace has made the Greeks “as great as possible and happy, and . . . useful to their friends and strong”) suggests that at least some Greeks thought that these agreements could indeed contribute positively to the stability and prosperity of the region. More specifically, the autonomy clause and related clauses, such as those banning the imposition of garrisons, might perhaps have constrained the excesses of powerful states against weaker ones, if only by making it more likely that a powerful state would face consequences for such actions.

Some have argued that the structure of the Common Peaces reflects more fundamental developments in Greek attitudes to war and peace. The first such development relates to the scope of these agreements. The Common Peaces were not universal, but their coverage was much wider than that of a conventional bilateral or multilateral treaty. The wording of the Common Peace of 387/6 implies that all Greek states (except those specifically excluded) would automatically be covered by its terms. Xenophon’s account of the second Common Peace of 371 suggests a more limited scope (in that Greek poleis have to actively declare their willingness to be involved in the peace: Xen. Hell. 6.5.1), but the open invitation to participate in the peace still marks a significant departure from standard Greek treaty-making practice. This feature of the Common Peaces has encouraged some scholars to see in them the earliest articulations of a system of universal principles of interstate conduct. The second possible development relates to the nature of “peace” itself. Whereas conventional treaty agreements were often (though not always) limited in duration, there is no evidence that the Common Peaces had any such restriction. In practice, no Common Peace endured for more than a few years; nevertheless, it has been argued that the open-ended nature of these agreements reflects a move towards recognizing peace not merely as an interruption between periods of war, but as a positive and at least potentially permanent state of interstate politics.