They then helped Potidæa, a Corinthian colony, but an Athenian tributary, to revolt from Athens. Corinth next appealed to Sparta, as the head of Hellas, to intervene ere it should be too late and check the Athenian aggression, which threatened to make her the tyrant of all Greece. At Sparta the war party prevailed, although King Archidamus urged that sufficient pressure could be brought to bear without actual hostilities. The great prosperity and development of Athens since the Persian war had filled other states with fear and jealousy. She had rebuilt her city walls and refortified the port of Piræus after the Persian occupation; Sparta had virtually allowed her to take the lead in the subsequent stages of the war, as having the most effective naval force at command. Hence she had founded the Delian league of the maritime states, to hold the seas against Persia. At first these states provided fixed contingents of ships and mariners; but Athens was willing enough to accept treasure in substitution, so that she might herself supply the ships and men. Thus the provision of forces by each state to act against Persia was changed in effect into a tribute for the expansion of the Athenian fleet. The continuous development of the power of Athens had been checked only momentarily by her disastrous Egyptian expedition. Her nominal allies found themselves actually her tributary dependencies, and various attempts to break free from her yoke had made it only more secure and more burdensome. Hence the warlike decision of Sparta was welcomed by others besides Corinth. But diplomatic demands preceded hostilities. Sparta and Athens sent to each other summons and counter-summons for the "expulsion of the curse," that is of all persons connected with certain families which lay under the curse of the gods. In the case of Athens, this amounted to requiring the banishment of her greatest citizen and statesman, Pericles. To this the Spartans added the demand that the Athenians should "restore the freedom of Hellas," and should specifically remove certain trading disabilities imposed on the people of Megara.