The Ionian rebellion postponed, for a time, Darius's designs on Greece, but the effect of it was to make the invasion more certain and more terrible in the end; for Athens, which was at that time one of the most important and powerful of the Grecian cities, took a part in that rebellion against the Persians. The Athenians sent forces to aid those of Aristagoras and Histiaeus, and, in the course of the war, the combined army took and burned the city of Sardis. When this news reached Darius, he was excited to a perfect phrensy of resentment and indignation against the Athenians for coming thus into his own dominions to assist rebels, and there destroying one of his most important capitals. He uttered the most violent and terrible threats against them, and, to prevent his anger from getting cool before the preparations should be completed for vindicating it, he made an arrangement, it was said, for having a slave call out to him every day at table, "Remember the Athenians!" It was a circumstance favorable to Darius's designs against the states of Greece that they were not united among themselves. There was no general government under which the whole naval and military force of that country could be efficiently combined, so as to be directed, in a concentrated and energetic form, against a common enemy. On the other hand, the several cities formed, with the territories adjoining them, so many separate states, more or less connected, it is true, by confederations and alliances, but still virtually independent, and often hostile to each other. Then, besides these external and international quarrels, there was a great deal of internal dissension. The monarchical and the democratic principle were all the time struggling for the mastery. Military despots were continually rising to power in the various cities, and after they had ruled, for a time, over their subjects with a rod of iron, the people would rise in rebellion and expel them from their thrones. These revolutions were continually taking place, attended, often, by the strangest and most romantic incidents, which evinced, on the part of the actors in them, that extraordinary combination of mental sagacity and acumen with childish and senseless superstition so characteristic of the times.