Such was the ordinary annual cycle of changes in the Copaic Lake in modern times, and we have no reason to suppose that it was essentially different in antiquity. But at all times the water of the lake has been liable to be raised above or depressed below its customary level by unusually heavy or scanty rainfall in winter or by the accidental clogging or opening of the chasms. As we read in ancient authors of drowned cities on the margin of the lake, so a modern traveller tells of villagers forced to flee before the rising flood, and of vineyards and corn-fields seen under water.
The plan of draining the Copaic Lake, which has been successfully accomplished within the last few years, was conceived and apparently executed at a very remote time in antiquity. Strabo reports a tradition that the whole basin of the lake had at one time been drained and cultivated by the people of Orchomenus, and this tradition has been strikingly confirmed by the recent discovery of a complete and very ancient system of drainage works in the bed of the lake. The discovery was made by the engineers charged with the execution of the modern drainage works. As described by them, the ancient works were composed of an ingenious combination of dykes and canals, which completely encircled the lake and, receiving the waters of the streams which flowed into it on the west and south, conducted them to the chasms on the east and north-east banks. Where the canal skirted closely the precipitous rocky shore of the lake, a single dyke or embankment sufficed, the water being led between the dyke and the shore. But where the canal had to cross a bay, or where the bank of the lake was not high and steep enough to serve as one side of the canal, two parallel dykes were constructed and the water flowed between them. The remains of these ancient drainage works in the bed of the lake are of two sorts. In the first place we see them as low broad mounds, about five feet high and fifty to sixty yards wide, stretching for long distances across the plain, either in an unbroken line or with occasional gaps. Sometimes it is a single mound that we see, sometimes two parallel mounds at a short distance from each other. And between the two parallel mounds or beside the single one a long shallow depression marks the line of the ancient canal. These long, low, broad mounds are clearly the remains of the dykes which formerly enclosed the canals, and which have been gradually reduced to their present level by the ceaseless wash of the waters in the course of ages. In the second place, the line of the ancient canals may be traced by the walls built of great polygonal blocks which in many places support and case the inner side of the dykes. In some places these walls are well preserved, but in others nothing of them remains but a conspicuous line of white stones running for miles through the otherwise stoneless plain.