12. Although we cannot here give a complete account of the great revolution which the irruption of the Dorians universally produced in the condition of the different races of Greece,(241) it may nevertheless be remarked, that a very large portion of the Achæans, who originally came from Phthia, retired to the northern coast of Peloponnesus, and compelled the Ionians to pass over to Attica. The reduction of the principal fortress of this country, the Posidonian Helice, is ascribed to Tisamenus; and that Helice was in fact the abode of the most distinguished families of the Achæan nation is evident from the legend, that Oxylus the Ætolian, at the command of the oracle, shared the dominion with Agorius, a Pelopid, who was descended from Penthilus the son of Orestes, and dwelt at Helice.(242) The chronological difficulty of Oxylus being called the cotemporary of a grandson of Penthilus is not of much importance. At Helice was also shown the tomb of Tisamenus, whose supposed ashes the Spartans (doubtless with the idea of thus making amends for the injustice of his expulsion) afterwards brought to their city, as they also did the corpse of Orestes at Tegea.(243) But hereupon follows a series of migrations to Æolis in Asia, which was founded in later times, in which the numbers of the Achæan race predominated. Although Orestes is called a leader of the first expedition,(244) he probably is only put for his descendants: Penthilus also is perhaps put only for that part of his descendants who went with the colony to Lesbos and Æolis. For all the Penthilidæ did not go; we find indeed Penthilidæ in Mitylene;(245) and others at Helice, as we have just seen. Pisander, a Laconian Achæan, is also mentioned as having gone with the expedition of Orestes; and there were men of his family in Tenedos at the time of Pindar.(246) Chapter IV. § 1. Physical Structure of Greece and Peloponnesus. § 2. Physical Structure of Arcadia. § 3. Of Laconia. § 4. Of Argolis. § 5. Of Achaia and Elis. § 6. Improvement of the Soil by artificial means. § 7. Early Cultivation of the Soil by the Pelasgians and Leleges. § 8. Numbers of the Doric Invaders. § 9. Mode by which they conquered Peloponnesus.