Consecration cross

Cross in Metnitz, Austria

Before the time of the reign of Constantine between 306 and 337, the consecration of buildings to facilitate mass had to be private for fear of persecution, so physical consecration marks are unlikely to remain. There are various opinions as to the beginning of formal and public consecration of buildings. One version says that from Constantine's reign onward, a consecration was a public celebration to be commemorated in the following years, so that visual symbols of this event, such as writing the Greek and Roman alphabets on the church floor, became possible.[3] Another version credits Theodosius I with starting the tradition between 379 and 395 by purifying pagan temples during the transition of the Roman Empire to Christianity.[4]

Consecration "imprints an indelible mark (St Thomas, II-II:34:3) on the building by reason of which it may never be transferred to common or profane uses." The physical mark of the consecration cross on the wall of a church signifies this.[3][5]

Cross in St Mary, Charlton-on-Otmoor

In the medieval tradition, the twelve interior crosses may be painted on plaster, or manufactured in an indestructible material and affixed to stone walls. The crosses tend to be placed high on the walls and to have a candle sconce fixed beneath. The twelve exterior crosses could be painted, engraved, carved or made of a different material and affixed.[3][5]

The most common and ancient form of four curved arms of equal length within a circle could easily be constructed by a stonemason using a compass. This shape is also called a rounded cross.[4][6] Its shape is not unlike the Bolnisi cross, cross pattée, iron cross and Canterbury cross. However the consecration cross exists in other traditional forms, such as the sun cross.[4]

Cross with candle sconce in Coimbra Cathedral, Portugal

Typically, there might be twelve painted crosses high on plaster walls within a church, and others engraved outside on door frames, pillars or corners. However this depends on the era, the form of Christianity, the ritual used, and the form of the building. Since the bishop sprinkles the altar and floor with holy water crosses also, it is not impossible that permanent commemorative marks may be placed there.[3][6][7] Some churches are very old and much changed, so in cases of good preservation one might find twelve crosses inside the earliest complete stone building, or a second set of twelve in a very large and reconsecrated rebuild where the new walls outsized the old.