The valley in which the city lies has no opening to the coast, and the water finds its way, often only with much care and artificial aid, through underground passages (katavothra) to the sea.
There are no affluents of any considerable size, and the only outlets are underground passages or katavothra extending for many miles through the calcareous rocks.
The north-east barrier was pierced by underground passages (katavothra) which carried off the overflow from Copais.
Though the Boeotian climate suffered from the exhalations of Copais, which produced a heavy atmosphere with foggy winters and sultry summers, its rich soil was suited alike for crops, plantations and pasture; the CopaIs plain, though able to turn into marsh when the choking of the katavothra caused the lake to encroach, being among the most fertile in Greece.
Save for a short period of prosperity under the Frankish rulers of Athens (1205-1310), who repaired the katavothra and fostered agriculture, Boeotia long continued in a state of decay, aggravated by occasional barbarian incursions.