Giovanni Battista Piranesi 

(Italian, 1720–1778)

“Illustrations of the Emissarium of Lake Albano,” 

VII from Descrizione e Disegno dell'Emissario del Lago Albano, 1762-64

Etching 

Gift of Margaret and Frank Robinson

This collage of “semi-engineering” images of Lake Albano, located southeast of Rome, shows various pieces of the tunnel and channel (called an emissarium) built to control the depth of the lake formed from a volcanic crater.  Controlling the depth is important to prevent flooding of the surrounding shoreline if the lake rises above its banks faster than the water can drain into the soil. Crater lakes typically have no outlet, so building drainage tunnels was common to control their height.

The upper right corner (Fig II) shows a cross section of the lake, providing scale to estimate the height of the hills and the distance needed to run the emissarium. The lake, which remains today, is approximately 560 feet deep and about 2.2 miles long and 1.4 miles wide. (Note that the letters A-H do not appear to correspond to the letters in the principal image.) The upper left corner (Fig I) seems to be the barrel-vaulted room shown from the outside in the lower left of the main image. The people in Fig I appear to be washing, or perhaps dyeing, cloth. The large tower dominating the main image does not seem to have a purpose in the operation of the emissarium. Perhaps it is a tower used to view the lake. It is not known when it was built and seems not to exist today. In the lower left, water flows from the lake in a spillway or sluice toward the tower and exits to be used in various ways such as irrigation, holding pools and so on. 

Ancient Romans are credited with building the emissarium. Apparently, water from Lake Albano surged over surrounding hills in 406 BC, destroying fields and crops. (If Piranesi’s image is to scale, then the hills are probably around 200 ft high.) The rain required to cause this flood would have been enormous, even with the largest of rain storms. One theory suggested that the crater bottom contained trapped gases from the original volcano, pushing the water over the banks and the surrounding hills. 

Approximately 11 years later (ca. 395 BC), Romans built a tunnel to control the depth of the water, which suggests the fear of the flood happening again was considerable. It was designed to act like the overflow drain in a tub, allowing water to exit before it flows over the lip of the tub. The tunnel – which still exists, but is obstructed at a multitude of points – is close to a mile long and about 6 feet high and 4 feet across. The volume of dirt and rock removed to create the tunnel was approximately 4,000 cubic yards. Nevertheless, the majority of the construction labor was devoted to building the stone walls of the tunnel. It apparently took more than 30,000 men to build the tunnel, which was likely over-designed to ensure the tunnel would permit very large water flow rates. 

The various figures (Fig I, II, etc.) show aspects of the tunnel that intrigued Piranesi, but do not provide particular insight into the construction details of the tunnel. Instead, the multiple images and detailed human figures show uses of the water by various villagers. Piranesi was a talented artist, but not an engineer.  

- Harvey Stenger, PhD (Engineering)

Search the database

To find objects in our permanent collection, search our database here.