Villa Adriana , declared a World Heritage Site by UNESCO in 1999, was built between 118 and 138 AD by the emperor Hadrian , in a green and water-rich area near Tivoli , the ancient Tibur. Villa Adriana in Tivoli extended over an area of at least one hundred and twenty hectares , including houses, baths, nymphaeums, pavilions and gardens . The various buildings were connected to each other, as well as by surface paths, also by a network of underground roads and sidewalks for services. The richness of the decorative apparatus was extraordinary, today dispersed among important museums and collections in Europe, following the looting. Currently the area that can be visited is about 40 hectares .