Sublaqueum
About
Nero dammed the Aniene river in three places above Subiaco, creating the Simbruina Stagna lakes that fronted his 75-hectare villa in the gorge. The tallest of the three dams reached roughly 50 meters, briefly the highest dam in the Roman world, and it kept holding its lake for over a millennium after Nero's death. Even after the emperor's fall in 68 CE, the lakes stayed intact in 117 CE. The largest dam finally failed in a 1305 flood; only Lago di San Benedetto survives today.
What happened here
Built to hold water for a town, a farm or a mine, and shaped by what the local rock allows: a straight wall of masonry backed with earth, or a curved one where the gorge is narrow. The core is concrete and rubble, faced in cut stone, and the upstream face is often waterproofed with mortar. Water is drawn from a tower with sluices at different heights, so the supply keeps running as the level drops and the silt stays at the bottom. Overflow channels carry the winter flood past the wall rather than over it — the detail that decides whether a dam survives. Silt is the long enemy; a reservoir has a working life and everybody involved knows it.
Sources
Roman Maps shows the empire frozen at 11 August 117 CE, the day Trajan died — its moment of greatest territorial extent. Explore the full map →