The Hegau is an extinct volcanic landscape in southern Germany extending around the industrial city of Singen, between Lake Constance in the east, the Rhine River in the south, the Danube River in the north and the Randen—as the southwestern mountains of the Swabian Jura are called—in the west. It was first mentioned in A.D. 787 in the Latinised form in pago Egauinsse. Wikipedia