a lake in the Campagna of Rome, near to Tivoli. It is of small extent, but is remarkable for containing several floating islets formed of matted sedges and herbage, with a soil of dust and sand blown from the adjacent country, and cemented by the bitumen and sulphur with which the water of the lake is impregnated. Some of these islands are more than forty feet long, and will bear five or six persons, who, by means of a pole, may move to different parts of the lake. From this lake there issues a whitish stream, emitting a sulphurous vapour, until it reaches the small river Teverone, which discharges itself into the Tiber. The water of that rivulet is of a petrifying quality, which increases in strength the farther it flows from the lake. Fish are only to be found in the Teverone before it receives this impure stream.