Santi Sisto e Domenico a Colle Parnaso is an earlier 20th century public chapel on Via Camus, in the small suburb of Colle Parnaso which is north-east of the junction between the Via Pontina and the Grande Raccordo Anulare (Circonvallazione Meridionale). The zone is Fonte Ostiense.
The chapel is on a green-field site near the junction of the Via Camus and the Via di Acqua Acetosa Ostiense.
The name is often rendered as Santi Domenico e Sisto.
The locality was once owned by the nunnery of Santi Domenico e Sisto, hence the dedication. The ownership is also commemorated by the Casali di San Sisto to the east, which is an old farmstead now in ruins after being derelict for some time. The roof collapsed recently.
Apparently this farmstead once contained a chapel, but there has not been a place of worship here for at least two centuries.
The present chapel was erected in 1920 by the Lanza family, as part of a scheme to develop their rural property as smaller farming units (coloni dell'agro).
Allegedly, the chapel was formally deconsecrated in 1970. The Diocese does not list it on its website.
However, the parish of San Mauro Abate advertise a Sunday Mass here and there are vague signs online of a local campaign to have its status as an official place of worship restored. There must have been a recent restoration, as the state of repair is good.
The location is picturesque, on top of a little hill and accompanied by some mature pine trees. The chapel is away from the road, and is accessed by a short rough trackway.
This is an attractive little neo-Baroque edifice on a rectangular plan, having a single nave of four bays. The side walls each have four round-headed windows, set low down. The corners are occupied with Doric pilasters. The background colour is a pale yellow, with architectural details in white. The main roof is pitched and tiled.
There is a tiny transverse rectangular apse, with its own much lower tiled roof. Inserted into the flank of this, at the far end of the right hand side of the nave, is an attached tower campanile on a longitudinal rectangular plan. Only the bell-chamber of this protrudes over the nave roof, and is in the form of a little rectangular pavilion with its own gabled roof aligned parallel to the major axis.
The façade has four Doric pilasters (including the corner ones) supporting a triangular pediment with a blank tympanum. The single entrance has a door-case in dark grey, with a crowning horizontal cornice. Aligned with this cornice are two lengths of molded string course connecting the two pilasters on each side. The four panels in between the pilasters thus created each has a slightly raised frame in white.
According to the parish website (July 2018), Mass is celebrated on Sundays and Solemnities (only) at 10:00.
Also, the Rosary is recited here at 17:00 on Mondays and Wednesdays.
(The online profile is surprisingly poor.)