16. Some of these plains become lakes, by rivers spreading over or falling into them and then flowing off. Some are dried up, and being very fertile, are cultivated in every possible way. But as the ground underneath is full of caverns and fissures, it has frequently happened, that violent earthquakes have obstructed some passages, and formed others under-ground, or on the surface, the water being carried off, either by subterranean channels, or by the formation of lakes and rivers on the surface. If the deep subterranean passages are stopped up, the waters of the lakes increase, so as to inundate and cover cities and whole districts, which become uncovered, if the same or other passages are again opened. The same regions are thus traversed in boats or on foot, according [CAS. 405] to circumstances; and the same cities are, occasionally, on the borders of, or at a distance from, a lake. 17. One of two things took place. The cities either retained their sites, when the rise of the water was insufficient to overflow the houses, or they were deserted and rebuilt in some other place, when the inhabitants, being frequently exposed to danger from their vicinity to the lake, released themselves from further apprehension, by changing to a more distant or higher situation. It followed that the cities thus rebuilt retained the same name. Formerly, they might have had a name derived from some accidental local circumstance, but now the site does not correspond with the derivation of the name. For example, it is probable that Platææ was so called, from πλάτη, or the flat part of the oar, and Platæans from gaining their livelihood by rowing; but at present, since they live at a distance from the lake, the name can no longer, with equal propriety, be derived from this local circumstance. Helos also, and Heleon, and Heilesium[350] were so called from their situation close to ἕλη, (Hele,) or marshes; but at present the case is different with all these places; either they have been rebuilt, or the lake has been greatly reduced in height by a subsequent efflux of its waters; for this is possible.