The draining of the Kopais Lake in Boeotia in the 14th century B.C. is the earliest drainage project in European history. Said by ancient writers to have been the work of the Minyans of Orchomenus, a rich and powerful Mycenaean kingdom on the western side of the Kopais basin, the project involved the construction of an elaborate system of canals leading to a central canal that drew off the water of the lake and emptied it into the sea at Larymna. The lake was fed by the Kephissus river and by streams from Mt. Helicon, and was surrounded by limestone mountains. A network of drains (katavothrai) in the stone, both natural and manmade, drained water from the basin into the northern part of the Euboean Gulf. The area was a shallow marsh in summer, with portions, particularly in the western part (the Kephisis), often dry enough to allow cultivation of the land. But the lake flooded periodically, to some extent annually and apparently extensively on a more or less regular nine-year cycle. The point of convergence of the Mycenaean drainage dykes with the artificial canal and the natural outlets (katavothrai) was near the location of Gla, the large Mycenaen site which was apparently not a palatial centre such as Thebes, Orchomenos, Mycenae, etc., but rather an administrative outpost which served both as protection for the area and as a depository for the produce of the fertile plain that surrounded it and that was available for cultivation while the Mycenaean drainage system was operational. The site of Gla itself was evidently “incorporated into the complex of drainage works and fortifications that surrounded it in antiquity, and was apparently the key point of the whole system”, its “main function [being] to protect the installations by which the lake was drained” (Iakovidis, 1983). When the lake was drained again in 1886 it was over three m deep in the area around Gla, which was consequently a true island, as the site would have been in the Mycenaean period prior to the drainage project. The method used in the 19th century drainage project reflected that of the second millennium B.C.: A system of dykes was constructed to hold back the waters running into the basin from the surrounding rivers, while the drainage outlets carried the lake water underground to empty into the sea.

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