Last evening, after Mass at Maiden Lane, a group of us were enjoying some good conversation and the topic of relics of the true cross came up. (At the time of the Reformation, it was commonly sneered that there were enough such relics to build a battleship, Noah's ark, a forest etc.) I knew that someone had actually researched the volume of all the known relics of the cross and had calculated that they would not amount to a single cross of the size used to crucify Our Lord. Looking up google today, I tracked down that it was Charles Rohault de Fleury who wrote Memoire sur les instruments de la passion in 1870.
As sometimes happens, I found another page that I thought would be worth sharing with you: James Franklin's Myths about the middle ages which covers many of the common ones.