Ostia, Oratorio di San Quiriaco is a small late 4th century ruined church just south-east of the theatre in the ruins of ancient Ostia.
The dedication was to St Quiriacus of Ostia (his name is also given as Cyriac).
This was the original shrine of St Quiriacus. He was a bishop of Ostia who was martyred in the town in the year 269 with seventeen converted soldiers, and it seems almost certain that an extant sarcophagus was re-used to hold his relics when they were enshrined here.
The oratory is on a complex site archeologically, and the ground level was raised substantially before it was built using re-used stone around the year 400. There is evidence of restoration using brick in subsequent centuries.
The shrine was recorded as still in use as a pilgrimage site in 1162, by which time it was probably the only intact building in the entire ancient town. However, it fell into ruin and was forgotten at an unknown date.
The relics of the saint were taken to a nunnery off the Corso named San Ciriaco after him, and when that failed and was suppressed in 1495 they were finally enshrined in the church of Santa Maria in Via Lata next door. He has a chapel in that church.
What survives of the church is part of the apse, and a stub of wall to the east.Many confused remains of burials were found around the building and below the floor, and the most interesting of these is a sarcophagus with strigillate decoration and with a relief of the Good Shepherd, which had an epigraph on the lid Quiriacus dormit in pace ("Quiriacus sleeps in peace"). This is plausibly regarded as having been the saint's shrine. The sarcophagus has been left in situ, but the inscription is in store for safe keeping.