In
Roman times, it was known as
Albanus Lacus and lay not far from the ancient city of
Alba Longa. With a depth of about , Lake Albano is the deepest in Lazio. The lake is long by wide, and was formed by the overlapping union of two volcanic craters, an origin indicated by the ridge in its center, which rises to a height of .
Plutarch reports that in 406BC the lake surged over the surrounding hills, despite there being no rain nor tributaries flowing into the lake to account for the rise in water level. The ensuing flood destroyed fields and vineyards before eventually pouring into the sea. It is thought to have been a
limnic eruption caused by volcanic gases, trapped in sediment at the bottom of the lake and gradually building up until suddenly releasing, causing the water to overflow.
Drainage tunnel Around 395BC, during the wars between Rome and
Veii, a discharge tunnel was built crossing the crater walls. It served as an
emissary to control flooding of the lake, and was a gigantic work given the modest means of the time. It is said that it was built by 30,000 men. The tunnel is 1350 m long, 1.20 m wide and 2 m high. Five vertical access shafts are known and it runs 128 m below the surface. The exit was originally 13 m below the level of the lake, but today it is higher due to the lowering of the level. It begins about 500 m beyond the nymphaeum of Bergantino, and comes out on the other side in the Mole di Castel Gandolfo locality, where the water flow drove multiple
watermills. According to
Titus Livius, this feat of engineering was incited by the
Oracle of Delphi: the Roman
victory against Veii would be possible only when the lake waters were channeled and used for irrigation. ==Lake Albanus in Roman myth==