(M371) The Spartans, after the conquest of Messenia, turned their eyes upon Arcadia—that land of shepherds, free and simple and brave like themselves. The city of Tegea long withstood the arms of the Spartans, but finally yielded to superior strength, and became a subject ally, B.C. 560. Sparta was further increased by a part of Argos, and a great battle, B.C. 547, between the Argives and Spartans, resulted in the complete ascendency of Sparta in the southern part of the Peloponnesus, about the time that Cyrus overthrew the Lydian empire. The Ionian Greeks of Asia Minor invoked their aid against the Persian power, and Sparta proudly rallied in their defense. (M372) Meanwhile, a great political revolution was going on in the other States of Greece, in no condition to resist the pre-eminence of Sparta, The patriarchal monarchies of the heroic ages had gradually been subverted by the rising importance of the nobility, enriched by conquered lands. Every conquest, every step to national advancement, brought the nobles nearer to the crown, and the government passed into the hands of those nobles who had formerly composed the council of the king. With the growing power of nobles was a corresponding growth of the political power of the people or citizens, in consequence of increased wealth and intelligence. The political changes were rapid. As the nobles had usurped the power of the kings, so the citizens usurped the power of the nobles. The everlasting war of classes, where the people are intelligent and free, was signally illustrated in the Grecian States, and democracy succeeded to the oligarchy which had prostrated kings. Then, when the people had gained the ascendency, ambitious and factious demagogues in turn, got the control, and these adventurers, now called Tyrants, assumed arbitrary powers. Their power was only maintained by cruelty, injustice, and unscrupulous means, which caused them finally to be so detested that they were removed by assassination. These natural changes, from a monarchy, primitive and just and limited, to an oligarchy of nobles, and the gradual subversion of their power by wealthy and enlightened citizens, and then the rise of demagogues, who became tyrants, have been illustrated in all ages of the world. But the rapidity of these changes in the Grecian States, with the progress of wealth and corruption, make their history impressive on all generations. It is these rapid and natural revolutions which give to the political history of Greece its permanent interest and value. The age of the Tyrants is generally fixed from B.C. 650 to B.C. 500—about one hundred and fifty years.