A recent study by C. Ohlig and D. Vieweger (Die Wasserkultur der Villa Hadriana, edited H. Fahlbusch [Siegburg 2008] 349-395) has a shed new light on this part of the villa, long known as Inferi after the passage in Spartianus' Life of Hadrian 26 dedicated to the villa. The 135 m long, 18 m wide depression forming the area was an ancient tuff quarry. At the southern end a grotto-nymphaeum was carved into the rock with flanking tunnels. The grotto was extended with a brick construction in front. No evidence has been found that would allow us to date the structure.