The Peace of Callias (c.448 BC) was almost certainly a formal peace treaty between Persia and the Athenian-led Greek alliance that ended half a century of open conflict between the two powers, and established their spheres of influence in the eastern Mediterranean (Greco-Persian Wars).
The peace was probably negotiated by the Athenian diplomat Callias, who had fought at Marathon in 490, and later helped negotiate the Thirty Year's Peace with Sparta that ended the First Peloponnesian War. He was probably given his opportunity in Persia by a Greek naval and land victory won at Salamis on Cyprus (c.451 BC), and that convinced Artaxerxes I (son of Xerxes I) to end the war. Some ancient sources connect it to the earlier naval victory at the Eurymedon River (466 BC), but not convincingly.
The generally accepted terms of the treaty (if it existed) created Greek and Persian spheres of influence. The Persians agreed to accept the autonomy of the Greek states in Asia Minor, to keep their troops three day's march from the coast (a line just to the west of Sardis), to keep their naval forces east of a line running through Phaselis and the Chelidonian islands in the Mediterranean and east of the mouth of the Bosporus in the Black Sea. The Greeks would keep their fleets west of the same lines, wouldn't attack or ravage any Persian territory and would keep the cities of Asia Minor unfortified.
The evidence for the treaty is rather vague. Herodotus, who was writing in the years before 430-425 (the date of the last events mentioned in his work), doesn’t mention it, although he does put Callias in the Persian capital Susa during the reign of Artaxerxes (464-425 BC).
Thucydides didn't mention the treaty, but he does say that the cities of Ionian were unfortified early in the Great Peloponnesian War, 431-404 BC (mentioned during the account of the fourth year of the war). Given the warlike nature of the ancient world this must have been the result of a treaty of some sort.
Demosthenes makes several references to the treaty. In On the False Embassy of 343 BC he refers directly to Callias as the negotiator of the celebrated peace and gives some of the terms (the Persians to keep their men one day's ride from the coast and the line at sea). He also says that Callias was later put on trial for taking bribes during his embassies, nearly executed and fined 50 talents instead. He doesn't expressly link the trial to the treaty with Persia. Attempts to suggest that the treaty was unpopular in Athens because of this trial also fail to convince - the Athenian people seem to have put almost all of their successful leaders on trial at least once.
Diodorus Siculus give the most detailed account of the treaty, but it comes at the end of a section on the campaign on Cyprus that doesn't match other sources. His version records a two-year campaign, with a major naval victory off Cyprus and land victory in Asia Minor in the first and a siege of Salamis in the second. This siege convinces Artaxerxes to come to terms.
Diodorus then lists the terms of the treaty. Again the Persians agree not to come within three days of the sea, not to sail west of the Cyanean Rocks and Phaselis, and that all Greek cities are to live under their own laws. In return the Athenians promise not to send their troops into territory ruled by the Persians.
Diodorus makes some further references to the treaty. In one he compares it to a vow made before the battle of Plataea (479) in which the Greeks promised to remain hostile to Persian for ever, a promise they had broken by negotiating a treaty with Artaxerxes son of Xerxes. In a second reference his mentions a treaty between the Persians and the Athenians, agreed at roughly the time when Diphilus was Archon of Athens (442-441 BC) and Marcus Horatius and Lucius Valerius Potitus were consuls of Rome (449 BC).
Plutarch mentions the treaty in his life of Cimon. He supports the idea that the treaty was agreed in the aftermath of Cimon's victory at Salamis on Cyrus. As a result of this defeat Artaxerxes agreed to a treaty in which he agreed to keep one day's ride from the Hellenic sea-coast and not bring his warships west of the Cyanean and Chelidonian isles. He also stated that a copy of the treaty could be found in a collection of decrees assembled by Craterus and that the Athenians built an alter of Peace to commemorate the treaty.
Even in the ancient world some believed that the treaty was fake. By the time Theopompus wrote his Philippicae, a history of the reign of Philip II of Macedon (360-336 BC) the Athenians had erected a monument to Callias on which the text of the treaty was inscribed. Theopompus noticed that the text used the Ionian alphabet, which was adopted in Athens in c.403 BC, nearly half a century after the treaty was said to have been concluded. However all this really tells us is a possible date for the monument (or even just the dialect spoken by the sculptor). It also confirms that the Athenians firmly believed the treaty to be real.
Plutarch records that Callisthenes also denied that any treaty had been made, but did acknowledge that Greek victories convinced Artaxerxes not to risk any attacks on the Greeks of Ionian.
In later years the Athenians portrayed the Peace of Callias as a major victory, and a significant Athenian contribution to the general good. It was followed by a significant period of peace between the Greeks and Persians, but that broke down by the end of the century, and from around 400 BC the Spartans were involved in a war against the Persians in Asia Minor (Persian-Spartan War).