Chiesaccia is a ruined mediaeval church in a field opposite the Pizzeria Arcobaleno, Via Laurentina 996 in the suburban zone of Vallerano.
There seems to be very little notice taken of this ruin, and there are apparently no published archaeological investigations.
On the hill to the south-east is a ruined mediaeval tower, the Tor Chiesaccia, and the surmise is that the two belong together historically. However, documentary evidence is also lacking.
The fabric is very tentatively dated to the 12th or 13th centuries. Another surmise is that the church belonged to a lost local village, but it is large compared to the usual small country churches of the Campagna. Alternatively it could have been intended for a monastery, but if so nobody knows any details.
A further oddity is that the edifice might never have been completed or roofed.
The edifice is within the ghost of a rectangular enclosure, itself in a large field containing a (now disused) farmhouse. It is in brick, on a rectangular plan comprising a single nave of seven bays with a large semi-circular apse slightly narrower than the nave. Each bay had a single vertical rectangular window in each side, fairly high up. The lintels of these, and the fabric above them, are lost.
The ruin has lost all the lintels of the windows and the fabric above them. Further, the façade has vanished except for a narrow fragment on the left hand side, and the right hand side wall has also gone for the first two bays. The façade fragment has what is either a buttress, or the remains of a side wall of an entrance loggia.
The field seems to be zoned for possible future development. It is fenced off and inaccessible. The interior of the church is full of scrub..