The Etang de Montady is an agricultural marvel that was created from a former freshwater wetland. It was constructed by Cistercian monks (a major civil engineering group in the late Middle Ages) during the second half of the 13th century. The Etang is located in southern France, midway between Beziers and Narbonne.
The 400-Ha area was drained by making radial ditches from the circumference down to a single center point. From the air the Etang looks like a giant bicycle wheel. Rainwater flows down the ditches to the center point and is then drained through an underground 1300-m culvert and tunnel system (the latter through Malpas hill). The individual field plots have a distinctive triangular, pie-slice-shaped configuration.
Seven-hundred years plus after its original construction, the drainage system is still operational.