=31.= The oldest of the oracles was that of Zeus at Dodona, where the message of the god was believed to be heard in the rustling of the sacred oaks and beeches, and interpreted by his chosen priests or prophetesses. At Olympia, in Elis, the will of Zeus was read in the appearance of victims sacrificed for the purpose. The oracles of Zeus were comparatively few. The office of revealing the divine will to man devolved usually upon Apollo, who had twenty-two oracles in European and Asiatic Greece. =32.= Of these the most celebrated was at Delphi, in Phocis, where was a temple of Apollo containing his golden statue and an ever-burning fire of fir-wood. In the center of the temple was a crevice in the ground, whence arose a peculiarly intoxicating vapor. When the oracle was to be consulted, the Pythia, or priestess, took her seat upon the sacred tripod over this opening; and when bewildered or inspired by the vapor, which was supposed to be the breath of the god, she uttered a response in hexameter verses. It was often so obscure,[37] that it required more wit to discern the meaning of the oracle than to determine the best course of conduct without its aid. But so great was the reputation of the Delphic shrine, that not only Greeks, but Lydians, Phrygians, and Romans sent solemn embassies to consult it concerning their most important undertakings. =33.= What Europe has been to the rest of the world, Greece was to Europe. The same peculiarities of coast and climate which made Europe the best adapted to civilization of all the continents, long made Greece its most highly civilized portion. But as Europe had her northern barbarians, always pressing upon the great mountain barrier of the Pyrenees, Alps, and Carpathians, sometimes bursting their limits and overrunning the more civilized but weaker nations to the southward, so Greece suffered, toward the close of the Heroic Age, from the incursions of the Illyrians on her north-western frontier. The time of this movement was fixed by Greek historians at sixty years after the fall of Troy, or, in our reckoning, B. C. 1124. Though the Illyrians did not enter central or southern Greece, their southward movement produced a general change among the tribes of the peninsula. The Thessalians, who had previously been settled on the western coast of Epirus, now crossed the Pindus mountains, and cleared for themselves a place in the fertile basin of the Pene´us, hitherto occupied by the Bœotians. The Bœotians, thus dispossessed of their ancient seats, moved southward, across Mounts O´thrys and Œta, to the vale of the Cephissus, whence they drove the Cadmians and Minyæ. These tribes were scattered through Attica and the Peloponnesus. The Dorians, moving from the northward, occupied the narrow valley between Œta and Parnassus, which thus became _Doris_; while the Dryo´pians, earlier inhabitants of this region, took refuge in Eubœa and the islands of the Ægean.