Now it is said that Thessaly was in old time a lake, being enclosed on all sides by very lofty mountains: for the parts of it which lie towards the East are shut in by the ranges of Pelion and Ossa, which join one another in their lower slopes, the parts towards the North Wind by Olympos, those towards the West by Pindos and those towards the midday and the South Wind by Othrys; and the region in the midst, between these mountains which have been named, is Thessaly, forming as it were a hollow. Whereas then many rivers flow into it and among them these five of most note, namely Peneios, Apidanos, Onochonos, Enipeus and Pamisos, these, which collect their waters from the mountains that enclose Thessaly round, and flow into this plain, with names separate each one, having their outflow into the sea by one channel and that a narrow one, first mingling their waters all together in one and the same stream; and so soon as they are mingled together, from that point onwards the Peneios prevails with its name over the rest and causes the others to lose their separate names.