Was a little forgery designed to convince the Holy Roman Emperors that the temporarl power of the popes in Italy stemmed from a grant made by the great Constantine himself, rather than one by Pepin the Short four centuries later. It didn't take long before the forgery was believed to be real, even by the Emperors, who therefore had to find innovative ways to try to assert a legal claim over papal lands. The forgery wasn't revealed until the 17th century, by Murator, a priest and humanist working in the Vatican archives.