Octagon Lake Cascade and Artificial Ruins

Benton Seeley's 1744 Guidebook opens with a description of the Octagon Lake and then highlights this garden structure as "An Artificial Piece of Ruin cover'd with Ever-greens, under which lie the Statues of two River Gods; a beautiful Cascade of three Sheets of Water falls from the Octagon into a large Lake of 10 Acres."
The Octagon Lake Cascade or Artificial Ruins
Bevington notes that three arches for a cascade were built in 1728-29 and that the artificial ruins decorating them were added by 1738, probably from a design by William Kent. Kent's Shell Bridge in the Elysian Fields, though far less rustic in appearance, has a similar design and serves a similar purpose as a dam and cascade between the Alder River and the River Styx.
faculty.bsc.edu/jtatter/cascade.html