According to writings of Socrates Scolasticus (born c. 380), Constantine's aged mother, Saint Helena, discovered the site of Calvary. There, her workers uncovered the timbers of three crosses1, a titulus and three nails, believed to have been from Jesus' Crucifixion.
To determine which piece of timber might have been used for Jesus, each was brought in turn to a dying woman. She recovered at the touch of the third timber, which was taken as a sign that this was the timber of the True Cross. (See also the The Old Rugged Cross.)
Fragments of the True Cross have been dispersed around the world and like the Relic Cross, True Cross fragments are venerated by Catholics and other orthodox Christians.
It is possible that this story gave rise to the superstitious phrase "Touch wood", for good luck.