To the east of the valley of Pheneus, and on the southern foot of Mount Cyllene, there is another lake basin, celebrated in antiquity because of the man-eating birds which infested it, until they were exterminated by Hercules. This is the Stymphalus, alternately lake and cultivated land. During winter the waters cover about one-third of the basin; but it happens occasionally, after heavy rains, that the lake resumes its ancient dimensions. There is only one katavothra through which the waters can escape, and this, instead of being near the shore, as usual, is at the bottom of the lake. It swallows up not only the water of the lake, but likewise the vegetable remains carried into it, and the mud formed at its bottom; and this detritus is conveyed through it to some subterranean cavity, where it putrefies slowly, as may be judged from the fetid exhalations proceeding from the katavothra. The water, however, is purified, and when it reappears on the surface, close to the seashore, it is as clear as crystal. There are many other lake basins of the same kind between the mountains of Arcadia and the chain of the Gaurias. They all have their swamps or temporary lakes, but the katavothras, in every instance, are sufficiently numerous to prevent an inundation of the entire valley. The most important of these lake basins is formed by the famous plain of Mantinea, upon which many a battle was fought. From an hydrological point of view this is one of the most curious places in the world; for the waters which collect there are discharged into two opposite seas—the Gulf of Nauplia on the east, and in the direction of the Alpheus and the Ionian Sea towards the west. There may exist even some subterranean rivulet which discharges itself, towards the south, into the Eurotas and the Gulf of Laconia. The disappearance of the waters underground has condemned to sterility several parts of the Peloponnesus, which a little water would convert into the most fertile regions of the globe. The surface waters quickly suck up and form subterranean rivers, hidden from sight, which only see the light again, in most instances, near the seashore, when it is impossible to utilise them. The plain of Argos, though surrounded by a majestic amphitheatre of well-watered hills, is more sterile and arid even than are Megara and Attica. Its soil is always dry, and soaks up water like a sieve, which may have given rise to the fable of the Danaids. But to the south of that plain, where there is but a narrow cultivable strip of land between the mountains and the seashore, a great river bursts forth from the rocks. This is the Erasinus.