San Ciriaco is a very obscure titulus or palaeochristian parish church, with the name titulus Cyriaci, thought to have been located under the present Finance Ministry in the rione Castro Pretorio.
One modern theory is that this name attached to Santa Maria Antiqua or Santa Maria in Domnica. However, ancient sources refer to the church as iuxta Diocletianas or in Thermis, which seems to indicate that it was near the Baths of Diocletian. it was founded in the early 5th century.
During the building of the Ministerio del Tesoro in the Via XX Settembre at the end of the 19th century, remains of a church were reported (and apparently not archaeologically recorded) at the south-west corner of the building site. This is north of what is now the junction between Via Cernaia and Via Pastengo. Although the evidence is not conclusive, it seems that this might have been the site of this church.
It is also not clear as to whether the remains were sealed within the foundations of the ministry building, or simply destroyed.