Early Church Fathers
36 "Oil of the cross" is spoken of not infrequently from the 6th century downward as efficient for healing. In the Itinerarium attributed to Antoninus of Placentia in that century mention is made of anipulloe of onyx stone containing oil being brought into contact with the wood of the treu cross which was supposed to be preserved in Constanine's Church on Golgotha, and the oil thereupon at once boiling over. It may have been oil which was believed to have thus acquired healing virtue that was originally meant by "oil of the cross." But in the following century we find notice of a belief that oil flow miraculously from the wood of the cross itself. For Adamnan, in his book De locis sanctis (which is mentioned by Bede, H.E.V. 15, as presented by him to King Aldirid of Northumbria, and published by Mabillon, de S. Adamn. Act. Benedict. soec. iii. part ii. p. 456), speaks of his informant, Arcuulf, a Gallic bishop, having seen at Constantinople, a piece of the true cross which had been sent thither by Helena, from the knots of which an odorous liquid with healing virtues flowed.
37 Filings from the supposed chains of St. Peter, preserved at Rome, were inserted in Keys for his sepulchre (cf. IV. 30), and these keys were sent by Gregory to various persons as valuable charms. Cf. I. 26, note 3.