I had no idea that such asserted relics were in the Paris Cathedral.
From today's Foxnews:
"A look at what is known about Notre Dame’s treasures and their fate.
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CROWN OF THORNS
Regarded as the cathedral’s most sacred relic, Paris Mayor Anne Hidalgo says the Crown of Thorns was saved. It is purported to be a relic of the crown placed on the head of Jesus Christ at his crucifixion, obtained and brought to Paris by King Louis IX in the 13th century. It is made of rushes wrapped into a wreath and tied with gold filament. Since 1896 it has been kept under glass and only occasionally displayed. Paris Deputy Mayor Emmanuel Gregoire said it was among pieces quickly transported to a “secret location” by officials after the fire. Hidalgo also said on Twitter that the tunic of St. Louis, a long shirt-like garment from the 13th century and believed to have belonged to King Louis IX, was also rescued.
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FRAGMENT OF THE HOLY CROSS AND NAIL
The 24-centimeter (9.45-inch) piece of wood and 9-centimeter-(3.5-inch)-long nail are purported to be from the cross on which Jesus Christ was crucified. The wood fragment is kept in a glass case. The fate of the two relics is not known.
Of course, in the Middle Ages, particularly, there were supposed relics of the New Testament events being sold and claimed everywhere. And the only one I think is likely authentic is the Shroud of Turin, because of it's impressive scientific analysis showing an ancient artifact unreplicable today, and certainly impossible to produce in the pre-science era.