The term Holy Thorn refers to every wooden fragment venerated as a relic because it is considered part of the so-called crown of thorns which according to the evangelical tradition was brought by Jesus. Christian tradition has it that this crown was recovered by Louis IX of France and then by he donated to the Cathedral of Notre-Dame in Paris. Over the centuries, numerous thorns were removed from this object to be donated to churches and sanctuaries for particular meritorious reasons.
Since 1633, whenever Good Friday falls on March 25, at least curious phenomena have occurred on that Holy Thorn: redness, swelling, greyish spots, in addition to the spectacular flowering that took place in 1852. The phenomenon is attested by notarial deeds bearing the testimony of personalities worthy of faith.
The Sacra Spina di Andria has acquired fame for the phenomena described above, even if these phenomena did not always occur punctually on March 25th. Green indicates the next year to the event, red if the year of the event is the current one.