The Hellenic league, formed to combat the Persians, was clearly headed by Sparta. Sparta presided at meetings and provided both land and sea commanders (King Leonidas at Thermopylae, Eurybiades at Artemisium and Salamis, Pausanias at Plataea, and King Leotychides at Mycale). After Plataea and Mycale (479), the Hellenic league dispatched the fleet once again. Under Pausanias' command, they went to Cyprus and subdued large parts of the island. They also took Byzantium, thus establishing Greek control over the entrance to the Black Sea.

The period from 479-431 is referred to as the Pentecontaetia (50-year period). Thucydides Book I is our main contemporary source. Plutarch and Diodorus of Sicily, both much later, are further important sources.

At Athens, the Athenians began rebuilding their walls. The Spartans opposed the rebuilding. Themistocles tricked the Spartans by delays until the Athenian walls were rebuilt. Clear lines of power and strategic moves. Themistocles also persuaded the Athenians to fortify the Piraeus. In 476 he was choregus for Phrynichus' tragedy The Phoenician Women, which dealt with an aspect of the Persian war.

The Athenians Cimon (son of Miltiades who had held command in the Chersonese) and Aristides, encouraged dissension in the Greek fleet. Pausanias was recalled home, and the Greeks refused to be under the command of his replacement, Dorcis. Pausanias was perhaps encouraging the Helots to revolt, and the Athenians did not care to have a Spartan in command: it is no surprise that he was killed by the Spartans and history calls him a Medising traitor. But in the 470's, he evidently returned to the Hellespont region and held some sort of command until he was recalled. Perhaps he was sent there to disrupt Athenian plans. His death is interesting:he took refuge at a temple, was walled up in it and then was dragged out just before death to avoid polluting it.

The Athenians took command and began to establish what came to be the Delian League. The Hellenic League, under Spartan leadership, continued until 462. The Delian league was a new alliance against the Persians, but under Athenian leadership. Clear lines of power and sides again. In winter of 478, the Delian League was officially formed on the island of Delos. It was to be a permanent league set up t fight Persian and exact recompense for the losses suffered in the Persian War. Each state had an equal vote, regardless of size. Some city-states contributed ships, others money. Aristides was in charge of establishing the rates (he is hardly heard of after this point). A treasury was set up on Delos and Athenians were in charge of it. We have annual tribute lists surviving, but only from 454 onwards.

It is not clear exactly how it all worked, but Athens had more and more resources at her disposal as time went on. For instance, when cities like Naxos, Thasos, and Samos revolted, they were subdued. Presumably from that point on, Athens used their dockyards. By 450/449, there was an accumulation of 5,000 talents of silver in the treasury (more on that later). Each state was supposed to remain anonymous.

The Delian league's first action, in 476/5, was to take over Eion, a Persian fortress on the Strymon river. Cimon, son of Miltiades, commanded. Next the Athenians expelled pirates from Scyrus (near Euboea) and settled it themselves. A few years later, they subdued Carystus, a Euboean city that had medized during the Persian war. Then in 467, Naxos revolted and was subdued. The pattern is clear: attack Persians, take over territory, force a city to remain in the league. Athens was beginning to be imperial. Secession from the Delian League was not an option. Revolt was quelled and one became subject to Athens. Cities were pressured into abiding by their commitments to tribute. Cimon is credited by Plutarch with the policy of converting allies from ship-contributors to cash-contributors to the league. In that way, Athens held the power and the allies were demilitarized. By 454, our first lists of tribute, only 17 cities still contributed ships, and by a decade later, only the islands of Lesbos, Chios, and Samos contributed ships.

Themistocles was ostracized in 474, 473, or 472. He was Cimon's rival. Cimon favored a policy of fighting Persia and cooperating with Sparta. Themistocles opposed Sparta. Themistocles moved to Argos, Sparta's rival on the Peloponnese. Sparta demanded that Themistocles be punished for "medizing," which is preposterous, but the Athenians assented. Themistocles may have been involved with Pausanias' efforts to rile the Peloponnesians against Sparta. Themistocles, however, fled first to Corcyra, then to Admetus, king of the Molossians, then to Macedon, then to Ephesus and Artaxerxes, son of Xerxes, who had come to the throne in 465/4. Artaxerxes made him governor of Magnesia on the Maeander. He died about 459.

Naxos' revolt was probably in 467. In the year following, Cimon led the Athenian fleet to victory at the Eurymedon river in S. Asia Minor. He captured 200 triremes and defeated the Persian army. Thasos revolted in 465. The Thasians resented Athenian actions in their vicinity (Eion and planned colonies). The Athenians besieged the city for 3 years and took it, in a clearly economically motivated imperial move. The Athenians also sent settlers to Amphipolis (or Ennea Hodoi) in 465, who were defeated by Thracians at Drabescus. Later, in 437, the Athenians refounded Amphipolis. From this defeat, the Athenians for the first time buried their dead in one grave all who had died for Athens without distinction of rank or family. There was a funeral oration. Such an action must have been approved by a decree of the people, perhaps put forth by Ephialtes and Pericles.

At this point (late 460's), there was a large earthquake and a helot revolt in Sparta, which explains why the Spartans did not help the Thasians. The Athenians helped Sparta to quell the revolt of the helots, but in a later revolt, the Spartans send the Athenians alone away. Perhaps the Spartans were worried about Athenian complicity in the revolt. Athens made an alliance with Sparta's enemy, Argos, and with the Thessalians, and that marked the final end of the Hellenic League in 462/1. Also, with Cimon off to aid the Spartans, Ephialtes and Pericles stripped the council of the Areopagus of most of its powers, a big move for democracy. Although Cimon was friendly to Sparta, his naval policies and his democratic increase of the power of common Athenians both tended to increase the divide between Sparta and Athens. In 461, Cimon was ostracized, and Ephialtes was assassinated by anti-democrats.

The road was open for Pericles' rise. Pericles was the son of the Alcmaeonid Agariste, and Xanthippus, the Athenian commander at Mycale.

When the helots who were revolting around Mt. Ithome surrendered, probably in 461/0, Athens settled them at Naupactus, which gave Athens an important base on the Western end of the Corinthian gulf.

War with Persia continued until the "Peace of Callias" in 449.

The Megarians withdrew from alliance with Sparta and went into alliance with Athens. Athens thus gained an important base on the Eastern end of the Corinthian gulf, and also was able to block the Isthmus of Corinth.

In the years after 460, the Delian League became the Athenian Empire.

From 460-454, the Athenians fought in Egypt against the Persians. They were defeated when Artaxerxes sent a large force against the Egyptians.

From 460 to 445, the "First Peloponnesian War" was fought between Sparta and Athens. 445 was the date of the 30 Year's Peace. In that war, Athens defeated the Aeginetans and besieged Aegina (remember that hostilities had been halted at the formation of the Hellenic League). That was the first time that the Delian League was used for purely Athenian ends, not against barbarians. Pericles was probably a leader in the effort against Aegina. While the siege of Aegina was ongoing, the Corinthians invaded Megara, but the Athenians sent their old and young reserve troops and held Megara. In 457, the Spartans entered the fray: a battle at Tanagra in Boeotia occurred. The Spartans won, but 62 days later, the Athenians, since Sparta had withdrawn, invaded Boeotia and were victorious at Oenophyta. That marked the beginnings of an Athenian Land Empire, which was to last a decade.

The Athenians built walls connecting the Piraeus to the Athens.

Delphi was a football in the wars: the Spartans liberated Delphi from the Phocians, but the Athenians put it under control of the Phocians again. This happened twice.

In 454, the treasury of the Delian league was moved to Athens. This might have been possible because of Persian threats in Egypt and Asia Minor. Athenian rule over allies was growing more and more harsh.

Cimon may have returned from exile in 451, but possibly earlier. He was sent on a naval expedition to Cyprus, but he died.

The "Peace of Callias" of 450 is not attested by any contemporaries, but it makes best sense of the end of hostilities between Athens and Persia. Cimon would have opposed peace, but Pericles favored it. Pericles' priorities were imperial expansion and to grow Athenian prestige and power. He must have thought that the "5 Years Peace" with Sparta was bound to end with a resumption of hostilities, and presumably war with Persia was more than he thought could be handled. Athens had been spreading herself too thin: Egypt, Peloponnese, Persia, etc. ThePeace of Callias put an end to war with Persia, but it also removed the raison d'etre for the Delian league. Many allies did not contribute their tribute.

Peace with Persia was a crisis for Athens. Pericles responded by passing the COngress decree, which invited the Greeks to a congress to discuss what to do with the 5,000 talents accumulated by the Delian League. Among Pericles' proposals were spending it to rebuild temples sacked by the Persians, fulfill vows made in the Persian war, and keep the sea free for commerce. Sparta had no interest in any of these, because they all would have meant putting Athens in charge and spending the money on Athenian building. But as propaganda, it was brilliant. Sparta responded by "liberating" Delphi from the Phocians. The Athenians later in the year put it back under Phocian control. Pericles also passed a decree, which we know about from a CE 100 papyrus commentary on Demosthenes' speech Against Androtion. The decree called for building the Parthenon and the Propylaea with the money in the treasury of the Delian league.

Athens managed to pull of the continued collection of tribute. Without war with Persia, the Delian League was no longer a pretense: Athens was openly an empire. Athens settled cleruchies (citizen colonies) and other colonies in many places. Also, new more stringent rules for tribute collection were passed. The currency of the empire was made uniform.

In 447/6, Athens lost her land empire in Boeotia, but managed to hang onto Euboea.

IN 446/5, the Thirty Year's Peace between Athens and Sparta and their allies was signed. Athens had to set Aegina free (it could still pay tribute, but Athens would not run it), lost Megara and its ports. Athens kept Naupactus, and control over Aegina. Athens probably accepted those terms because of the threat of Spartan invasion of Attica and because of the recent revolt of Euboea and Boeotia. Athens gained recognition that she controlled her empire: she signed for the entire empire. Pericles' policy in the ensuing years was to strengthen the Athenian navy and empire.

Samos, theoretically an equal ally of Athens, had gone to war with Miletus. Athens ordered the Samians to submit to arbitration. Samians refused. Byzantium too revolted. Athens besieged Samos. Samos fell. Democracy installed on Samos instead of oligarchy. The situation was serious, because Samos might have been helped by the Persians and the Black Sea trade route was at stake.

In 437, Amphipolis was founded as an Athenian colony on the Chalcidice. It grew to be an important city, because of the natural resources it could draw on: timber, pitch, metals. The empire was a self-propelling device in terms of economy and military. The fleet was an economic and military tool.

Pericles was convinced of the need for unity and organization, and that the Athenians should be the leaders, because of their vitality and enlightened government.

Was Athens' empire inevitably caused by circumstances?