The ruins contain specimens of almost every kind of construction. The most ancient part is a wall of opus incertum, composed of small polygonal fragments of tufa, which stands near the Casino Fede. This wall is probably a remnant of some older villa rustica or farmhouse which occupied the site before Hadrian’s time, and may have belonged to the gens Ælia. It apparently belongs to the first half of the first century B.C. The most common mode of construction is opus reticulatum, with squares of tawny coloured tufa cut in the valley adjoining and bonded at the corners with blocks of the same rock, or with red bricks. In those parts of the buildings, which require great durability from being exposed to the action of water, brickwork is used throughout. The Greek theatre and parts of the academy are built of small squared blocks of tufa, or in some cases of irregular fragments of tufa resembling the later opera Saracenesca. These are sometimes strengthened with bands of reticulated work. In most cases the outer covering of the walls has been removed, especially where it consisted of marble slabs. Some of the stucco ornaments are still very beautiful and well preserved. Each part of the buildings is complete in itself, but they do not seem to have been arranged on any general plan, and now that the roads which conducted from one part to another have disappeared, they present a confused mass which requires some careful attention to unravel. I have been obliged to confine myself to a very general and cursory account of each main feature. To notice every detail would be far beyond the compass of this book. In Ligorio’s plan 334 different parts of the villa are marked and separately described, and he spent a year in his investigation of the ruins. Spartianus gives us the names of the Lyceum, the Academy, the Prytaneum, the Canopus, the Pœcile, the Tempe and the Inferi as the parts of the villa made by Hadrian in imitation of their foreign originals. To these Ligorio has added the name Cynosarges found upon a brick stamp. The sites of the Canopus, the Pœcile, the Academy, Tempe, and the Inferi may be said to be ascertained with tolerable certainty, but those of the Lyceum and Prytaneum have not been discovered. The other names given by antiquarians to the different buildings are generally founded upon some definite evidence drawn from their shape and situation, and are probably upon the whole fairly applicable. They are the Theatres, the Palæstra, the Nymphæum, the Library, the Imperial Palace, the Hospitals, the Stadium, the Camp, and the Thermæ.