Santa Maria Immacolata a Villa Borghese is a late 18th century church (originally private) on the Piazza di Siena in the park of the Villa Borghese. This is in the Pinciano quarter. Picture of the church at Wikimedia Commons. 
The dedication is to the Immaculate Conception.
in the late 18th century, Prince Marcantonio Borghese commissioned the architect Mario Asprucci to re-model the Casina in the neo-Classical style, and to include a small church in the fabric. This was part of the prince's massive re-organization of the country seat of the Borghese family. The specific intention here was to provide a place of worship for the servants and employees of the Villa Borghese, rather than have them go down to Santa Maria del Popolo which was the nearest parish church.
The church was finished in 1792.
In 1829, Prince Camillo Borghese employed Luigi Canina to restore the church, which had apparently been stripped and left in disrepair. The interior was frescoed by Pietro Carrarini. This again was part of a larger project of upgrading the villa's grounds, and Canina was also responsible for the monumental gateway on the Piazzale Flaminio.
In order to place the future of the church on a secure footing, in 1839 Prince Francesco Borghese established a trust fund in order to pay the salary of a priest and to provide the necessities for the sacristy. However, the church remained a private institution for the rest of the century.
In 1903, the gardens were bought by the municipality and formally opened to the public. However, the casina containing the church remained in the occupation of a private tenant.
In 1933, the church was put under the authority of the parish priest at Santa Teresa d'Avila , who became responsible for the celebration of Mass here. This arrangement continued until 1997, when it was decided that the arrangement was no longer pastorally justified. The Vicariate of the Diocese has provided the priest-in-charge since then.
The continued occupation of the casina by private tenants became grossly unsatisfactory towards the end of the 20th century. Arrears of maintenance had made the building unsafe, especially in the area of the church portico. However, possession was obtained by the municipality which undertook a major restoration in 2003.
The casina now contains a ludoteca or toy library, opened in 2006.
The church is now available for weddings, although its size precludes a large congregation. Otherwise, it must struggle to justify its pastoral existence and its future as a consecrated building in the long term must be in some doubt. There is a website, but it was last updated in 2005 which itself is a cause for some concern.
The casina is oriented south-east to north-west, with the main entrance at the former. The ludoteca is here. The north-west side is the church entrance. The plan of the edifice is rectangular overall, and its elevation is two-storey. The south-western part has four two-storey wings around a very narrow courtyard, and the north-western part has one storey except for the church.
The entrance façade is single-storey, is three times the width of the single-naved church behind and is faced in limestone ashlar. There is an internal loggia, entered through an impressive neo-Classical portico consisting of four grey granite Doric columns supporting an entablature which is continued to each side across the entire façade. The frieze of the entablature is embellished with triglyphs.
The columns are classic Doric in the ancient Greek order, and they do not have bases. Most "Doric" architecture in Italy is of the developed Tuscan variety, and this colonnade is thought to represent the first modern use of the Greek version in Italy.
The simple frontage of the church, with a triangular pediment and round-headed window, peeps over the façade. The window is in a recessed arched frame with Doric imposts, and the pediment is supported by Ionic pilasters at the outer corners. The cornice of this is broken just within the pilaster capitals.
There is a terrace between the church frontage and the horizontal roofline of the façade, which unfortunately requires an ugly metal railing safety barrier. But at least the recent restoration has finally got rid of the tenant's horrible collection of potted trees on the terrace, in front of the church frontage.
The tiny rectangular interior has three bays. It was restored in 1828, and the ceiling provided with frescoes by Pietro Carrarini.
This barrel-vaulted ceiling has three large central tondi, and three deep lunettes on each side that reach the tondi and are truncated by them. Tondi and lunettes are bounded by ribs painted with flower gardens, and the lunettes and panels between them are alternately painted in pale blue and light grey. These zones each contain a figure of a saint or prophet, within a little painted aedicule. The central lunette shows angels in heaven, and the two side ones have fronds.
The ceiling rests on a cornice that runs round the church. The side walls are either plain, or revetted in a striped light grey and white marble.
The altar has a small aedicule with a triangular pediment supported by a pair of granite Ionic columns. The altarpiece is a statue of the Immaculate Conception by Guillaume-Antoine Grandjacquet. Above the aedicule is a wall lunette with a fresco of God the Father Venerated by Angels. In the corners either side of the altar are folded pilasters in the same marble as the side wall revetting.
Mass is celebrated at 12:00 on Sundays.
Church website (contains bad links)