For millions of Christians, the Shroud of Turin is one of the most revered religious icons in the world. The shroud is a 14-foot piece of linen fabric that was purportedly used to wrap Jesus's body for burial. Most remarkably, the shroud features a negative image of an adult male, supposedly Jesus himself. The image, some have suggested, is actually an incredibly detailed bloodstain left by Jesus's body. Since 1578, the shroud has resided in the cathedral of San Giovanni Battista in Turin, Italy, where it attracts thousands of visitors each year.

To some, the validity of a religious icon is a matter of faith, not science. But thanks to modern carbon-dating techniques, scientists have been able to prove that the Shroud of Turin couldn't have been Jesus's actual burial shroud. The Bible doesn't specify exactly what year Jesus perished, but most scholars agree it was the year 33 AD. In 1988, carbon-dating showed that the Shroud of Turin originated in the Middle Ages. Forensic scientists also examined the blood spatter patterns on the shroud and concluded they were made by someone sitting in a variety of positions, not lying flat like a cadaver.

Traditionally, churches and cathedrals like San Giovanni Battista have displayed holy relics purportedly belonging to Jesus, the saints, and other important religious figures. These holy relics weren't just objects of worship, but also big moneymakers that attracted thousands of pilgrims, just like they do today. Like the Shroud of Turin, the provenances of these relics are impossible to prove. In more recent years, the Vatican has officially classified the Shroud of Turin as "an icon" rather than a literal holy relic.