The villa is located in a valley rather than high on a hillside as many Renaissance villas are.
According to Vasari, the design of the Villa Giulia was a collaborative effort that involved Vignola, who was commissioned in 1551, Ammannati, who came to the project after it had been begun, and Vasari himself. Vignola seems to have designed the palace section and its semicircular court, and Ammannati is credited with much of the rest including the gardens. Vasari, who claimed credit for the plan, performed many of the administrative tasks. Pope Julius, who frequently consulted with Michelangelo, also participated in determining aspects of the design.
Today the Villa Giulia is used as a museum of Etruscan art. Among its treasures is a sarcophagus whose lid is ornamented by portraits of the deceased couple in the reclining posture of the ancient Greeks when dining or partying.
The interior was richly decorated with features like frescoes on the ceiling.
The main spaces of the Villa Giulia's inwardly focused design are laid out along a central axis. They become increasingly smaller in scale as they approach the rear.
The entrance section is blockish at its front and semicircular at its rear, where it forms one end of a long court. Walls at the sides connect the entrance building with the building containing the nymphaeum.
There are several changes of level between the entrance to the nymphaeum and the nymphaeum itself, which is underground.
Despite the active participation of several architects, there is an overall unity, which speaks well of the ability of its designers to coordinate their ideas.
One unifying element is the repetition of similarly shaped areas that are arranged in similar configurations.
The Villa Giulia is located in a valley rather than on a hillside, where Renaissance villas were usually placed.
In its compactness, the façade of the Villa Giulia resembles a Renaissance palace.
Because of the contrast in plasticity and color between the central three bays and the outer bays, the façade reads as three distinct parts. (Although they are apparent in a frontal elevation, only the edges of the lateral wings are visible from the front due to perspective.)
A secondary three-part arrangement exists in the treatment of the three central bays.
Vignola's three-bay entrance is far more plastic in its projection from the plane of the main block than the outer portions of the façade, which consist of plain stucco walls around ornate windows.
Rustication is used on the columns, pilasters, and arches of the lower story of the Villa Giulia, where it creates coarser counterparts to the more refined elements on the upper story such as thin Corinthian pilasters.
Because the villa was located outside the city walls, the fortified look of the gate-like rusticated entrance may have been intended to express a defensive capability.
The large window above the door opened out to a balcony with a prominent balustrade.
The semicircular end of the courtyard, which is formed by the rear of the entrance wing, is entered through a vestibule. The semicircular loggia, which is constructed as an annular vault, is an early manifestation of Vignola's preference for curving forms like the circular courtyard and spiral staircase realized at his later villa, the Villa Farnese.
A concave version of the triumphal-arch motif, which was used for the three-bay unit forming the entrance, is repeated in the center of the semicircular court. The two bays at each end resemble incomplete, two-bay versions.
Two sizes of column are used on each story of the semicircular facing of the court. The larger, full-story columns take the form of superimposed pilasters on both stories. However, the smaller columns are freestanding on the ground floor and serve as supports for the loggia, while on the upper floor, they are pilasters that separate the windows and articulate the façade. The choice of orders, Corinthian above Ionic, follows the traditional upward progression from simple to more complex and ornate.
Although the courtyard's rectangular part is only one-story high according to the scale defined by the two-story semicircular section, it is articulated as two by a mid-level stringcourse. This division increases the shorter wall's continuity with the taller one. When seen from the entrance end, it magnifies the viewer's perception of the court's size because of the eye's tendency to perceive a continuity between the two walls because they lie on the same plane. The diminished size of the more distant wall will thus be attributed to greater distance rather than to smaller size.
The slightly elevated area between the upper and middle levels originally was enclosed by a wall containing a doorway leading to a loggia, but it has been remodeled to have column screens on both facings.
The nymphaeum complex is distributed over three levels, two of which are underground, where visitors can escape the summer heat while enjoying a series of views.
At the end of the upper court, a loggia acts as a vestibule that provides a view of the subterranean levels and access to a pair of curving staircases.
The curving staircases lead down to the lower levels but not to the ground-story loggia on the other side of the nymphaeum, which must be reached from the garden.
The nymphaeum on the lowest level can only be reached by the spiral staircases concealed in the walls. The invisibility of access adds to its allure.
A lotus pond encloses the lowest terrace, whose semicircular shape reflects the balcony overlooking it. Water flows from the Fontana Segreta (Secret Fountain), which is fed by the Aqua Vergine, an old Roman aqueduct that Julius III reactivated for his own use.
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Vignola's façade of the Villa Giulia, Rome, 1550-55
Ammannati's Nymphaeum of the Villa Giulia