Sparta and Athens, the two most powerful cities of Hellas, did not have much in common. The Athenians attempted to develop their artistic and intellectual capabilities, while Sparta remained isolated from the rest of Hellas, without art or literature, without beautiful buildings, without any development of their social and political traditions. Sparta lived on as a fossilized military city, though its military capabilities and more or less stable form of government still were admired by many other Greeks.

The walls of Piraeus.

The development of Athens as an aggressive leader of its own Delian League was closely followed by Sparta. Still, Sparta had cleared the road for an Athenian hegemony by retreating in a conservative isolationism in 478. The first signs of serious rivalry showed when Themistocles persuaded the Athenians to turn their city into an enormous stronghold to prevent another sacking like the one in 480 by the Persians. Another reason was that they would no longer have to be dependent of the much stronger Peloponessian land armies to protect their city. The fortification was a logical next step in the policy of Athens to become primarily a seapower. The most important constructions were two parallel walls from Athens to Piraeus which turned harbour and city into one huge fortress.

Sparta did envy the Athenian harbours Piraeus and Munichia, but they were no threat to Sparta itself as they were mainly used for the trade. The walls around Athens and towards the Piraeus were a completely different story. The only logical reason for their construction was that Athens had aggressive plans reasoned Sparta. Would Athens attempt to attack Persia? Then the Persian empire might see this as an attack from Hellas on Persia, and attack a city without these enormous walls, Sparta for example, as a revenge. But what if Athens did not have any plans to attack Persia, then it would surely try to attack Sparta.

Sparta send a delegation to Athens to prevent the construction of these walls. Themistocles promised that he would visit Sparta with a delegation to explain everything. However, he went alone to Sparta and ordered his colleagues to stay in Athens until the walls were finished. Once he arrived in Sparta he claimed that he could not do anything as he did not have the power of attorney. A while later his delegation arrived and they returned to Athens again with a group of high Spartans, so that they could convince themselves that the walls would not form a threat. When they were left Themistocles told the Spartans the truth: if Sparta would let him go unharmed, then the high Spartans who were now in Athens would return unharmed too. Sparta did not have much of a choice as it needed its full Spartans too much. Themistocles returned to Athens unharmed, and as a victor.

A desire for a balance of power.

Athens' aggressive policy towards Sparta changed when Cimon, the son of Miltiades, became an important politician in Athens. He had played an important role in the expansion of the Delian League, and had the same ideas about this as Themistocles. However, unlike Themistocles he was in favour of a balanced relationship between Sparta and Athens, and he did not feel anything for further democratisation like Themistocles did. The political and personal fight between the two men was decided in favour of Cimon when Themistocles was banished in 471 by ostracism.

Themistocles fled to Argos, which had become the centre of a movement in the Peloponesse that demanded more democracy. After a while the Athenians came to a paradoxical conclusion, which was inspired by Sparta: Themistocles, the man who had humiliated the mighty Persian empire, was accused of committing treachery with Persia. When the anti-democrats recovered their power in Argos he fled to Persia, where he was welcomed by the Persian king. He became governor of the Persian city Magnesia where he died in 462.

In 462 the Peloponesse was struck by a major earthquake, the result, a revolt of the helots which is known as the third Messenian war (464-459), was an even bigger disaster. Sparta was too weak and was forced to ask Athens for help. The democrats in Athens were against: no help for a possible enemy in the near future. The conservatives were in favour: keep Hellas strong to oppose the Persian threat. Cimon personally left with 4000 hoplites to convince Sparta of the good intentions of Athens. Pericles warned that Sparta was now forced to accept the Athenian help, but that it would only hate Athens even more for it.

When the Athenian army arrived it was sent back by Sparta. Maybe Sparta was strong enough again to end the revolt, maybe it did not trust Athens indeed. There were reasons enough for Sparta not to trust Athens as Thasos had ended its membership of the Delian League in 465, and was punished severely for it as a result. Sparta had promised Thasos help, but could not give it because of the earthquake. It is not surprising that Sparta rather did not accept Athenian help in this akward position. Nevertheless was this seen as an insult in Athens, and Cimon got banished by ostracism in 461.

An escalating conflict.

The banishment of Cimon was a return to the more aggressive policy against Sparta of Themistocles. In 459 Megara had a conflict about its borders with Corinth, and voluntarily joined the Delian League to get some protection. For Athens was this very important as Megara had two harbours, Nisaea at the Sardonic gulf, and Pagae at the Corinthian gulf. This gave Athens better access to the west, which was a threat to Corinth that still had the best contacts in the west. Athens gained an even better position in the west by founding Naupactus with a few Messian helots after the collapse of their revolt. In the first phases Corinth was more obviously to the front in fighting than Sparta, because of the adhesion to Athens from Megara, and as the new Athenian expansion to the west formed a threat to their trade.