ALSIETINUS LACUS (mod. LAGO DI MARTIGNANO), small lake, south Etruria, 15m. due N.N.W. of Rome, in an extinct crater. Augustus drew from it the Aqua Alsietina ; the water was hardly fit to drink, and was mainly intended to supply his nau machia (lake made for a sham naval battle) at Rome, near S. Francesco a Ripa, on the right bank of the Tiber. The aqueduct, mainly subterranean, is practically untraced. Frontinus tells us that it received water from the lake of Bracciano near Careiae (Galera) ; and an inscription relating to it has been found in this district, while the only known remains of the channel were found on the Janiculum in 2927.