The villa built by Emperor Hadrian occupies a large plain (extending 120 hectares) at the base of the Tiburtini mountains southwest of Tivoli.
The complex is a series of buildings of monumental character spread out among the green surroundings and blending intimately with them.
The perfect fusion of architecture and landscape and the articulation between the single building complexes and garden spaces is apparently casual (actually the fruit of a careful study of the setting) and makes Hadrian's Villa an exception in the history of ancient architecture.
The historic and artistic importance of the complex contrasts in a singular way with the almost total silence of ancient literary sources. Rare mentions of the complex led to traditions and legends which often were with no real historic basis.
A passage in a biography of the 4th century sustains that Hadrian called the different parts of the Villa with the names of the most famous places in the Roman provinces. Often this piece of information was interpreted to mean that the Emperor had had copies made of the sites he had visited. In reality, the buildings are not rigid imitations but autonomous and original creations inspired by famous models. Another legend sees the Tiburtine complex as a work of the Emperor's old-age, whereas it is certain that the Villa was built in the first years of his rule.
From a brief passage of the writer Aurelio Vittore, it can be deduced that the Emperor took part directly in the design of the Villa, confirming another piece of information which claims that Hadrian was both architect and mastermind behind the complex.
A first important datum is that on the sight of the complex another a villa from the Republican era once stood (2nd-1st century B.C.), and perhaps belonged to the wife of the Emperor, Vibia Sabina.
Hadrian's Villa developed around this more ancient nucleus, which was preserved as the heart of the imperial residence.

The Villa was built completely during the first 10 years of Hadrian's rule. In particular, it has been demonstrated that work began on it immediately after the arrival in Rome of the new emperor, in mid AD118. The phases of construction and the relative buildings can be synthesized as follows:

1st phase (118-125) Libraries; northern complex of the eastern buildings (basilica, library); the Courtyard of the Libraries; hospitals and annexes; garden southeast of the Palazzo (pavilion northeast of the Piazza d'Oro); the Baths with the Heliocaminus; the Maritime Theatre; the Stadium with annexes; the firemen's barracks; the Great Baths.

2nd phase (125-133) Small Baths; the central complex of the eastern palace; the western palace; the Tower of Roccabruna; the Piazza d'Oro; the Praetorium, the Vestibule; the hundred chambers and Poecile; the pavilion towards the Terrace of Tempe; the Canopus; the courtyard east of the stadium.
The buildings of the Villa are built mainly of mixed materials (pyramid-shaped blocks of tufa and strips of bricks) and at times of tile brick. One aspect of the Villa under study recently has been the existence of a system of underground tunnels for both vehicles and pedestrians. This system served as an underground service network which functioned independently from the upper level thus not interfering with the official and formal nature of the ground level.