An Aeginetan traitor, named Nicodromus, offered them his assistance, and, aided by the popular party opposed to the oligarchical government, he seized the citadel.
With twenty ships from Corinth, and fifty of their own, the Athenians invaded Aegina; but, having been delayed in making the adequate preparations, they arrived a day later than had been stipulated.
Nicodromus fled; the oligarchy restored, took signal and barbarous vengeance upon such of their insurgent countrymen as fell into their hands.

Meanwhile, the Athenian fleet obtained a victory at sea, and the war still continued.
XVIII.

While, seemingly unconscious of greater dangers, Athens thus practised her rising energies against the little island of Aegina, thrice every day the servants of the Persian king continued to exclaim, "Sir, remember the Athenians!" [272] The traitor, Hippias, constantly about the person of the courteous monarch, never failed to stimulate still further his vengeance by appealing to his ambition.
At length, Darius resolved no longer to delay the accomplishment of his designs.

He recalled Mardonius, whose energy, indeed, had not been proportioned to his powers, and appointed two other generals-- Datis, a native of the warlike Media, and Artaphernes, his own nephew, son to the former satrap of that name.

These were expressly ordered to march at once against Eretria and Athens.