The crater lakes of both Nemi and Albano had emissaria – tunnels to provide a water supply outside the crater - constructed in ancient times. In the case of Albano, a tunnel of 1,450 metres was constructed around the fourth century BC. Historic sources (Livy) claim that the Oracle of Delphi declared that the city of Veii would never be conquered by the Romans unless the Albano Lake was drained; so the Romans set to and did it.
The neighbouring Nemi Drain is believed to be even earlier and dates from the end of the sixth century BC. Measuring 1,653 metres long, it was constructed from the two portals without intermediate shafts. The lake end has two separate entrances, perhaps reflecting changing water levels through the ages. In places the tunnel has apparently been deepened maybe for similar reasons. Roughly half way and two thirds through the tunnel are ‘by-passes’ built either to get round earlier collapses or to avoid particularly challenging geology.
There is still a little water flowing through the tunnel and in places this flow contains speleothems in the form of fabulous cave pearls. The by-pass sections can be negotiated but are quite a tight squeeze and likely to be wetter than the main passage. There is also a water pipe through much of the tunnel, believed to date from the late 1920s when Mussolini drained Lake Nemi to recover two Roman Barges built for Emperor Caligula in the first century AD.
On reaching the end of the tunnel, the water would have been used for irrigation and for industrial purposes such as milling. Sub Brit was privileged to be given permission to explore this fascinating survivor with great assistance from Roma Sotterranea.