The Roman cistern at Affile is a rectangular shape (measuring roughly 3 x 17 M), covered by a barrel vault with very thick walls.
The submerged lower floor is entirely filled with water and in parts preserves traces of the original high walls on the southern and western sides, with reticulatum panels, while the other two sides of the  cistern were probably cut into the rock.
 
The water was collected from a circular opening in the centre of the vault, which was later plugged up.
 
Above the cistern, sources say that it was built on the ruins of a Church that Otto III had built in 999 and dedicated to Saint Michael the Archangel, Saint Benedict and Saint Adalbert, later known simply as Sant’Angelo. The Church had already disappeared by the 16th century. An ancient Roman column, currently in the cistern itself, may have been re-used in the Church.
 
In a cellar in the cistern there are also the remains of another building, with some of the high walls still visible and a floor made out of lime mortar with crushed bricks.