Roman Dam of Belas

Built in the 3rd century to serve Roman Olisipo, [this dam survives](https://en.wikipedia.org/wiki/Roman_Dam_of_Belas) only as a central segment reinforced by buttresses, but that remnant still conveys the scale of the original work. Its abandonment date is unclear. The ruins were identified in 1571 by the Renaissance humanist Francisco de Holanda, who even proposed reusing the dam and associated waterworks for Lisbon's supply.

Belas, Lisbon, Portugal