Phil Mason

“It went on to purport that Constantine – then based in the later Empire’s eastern seat in what would become Constantinople – had decided to site himself there because it would not be right for him to be located in the city where the head of the Christian faith reigned. The supposed donation was not revealed publicly until the mid-700s when it was used in 754 by Pope Stephen to negotiate with Frankish King Pepin about the division of lands between the two rival authorities. It was wheeled out again in 1054 when Leo IX was in dispute with the patriarch of Constantinople over the rights and powers of Roman rule. It became an essential document in later years as popes reacted to challenges against their authority in the growing post-Dark Age Europe in the 10th and 11th centuries. It was, though, entirely fictitious. Thought now to have been concocted by the papal chancery to provide retrospective authority for the increasingly strained church, it was not until the 15th century, nearly 700 years after its appearance, that scholars began openly questioning its veracity. It was finally debunked in 1518. It should have been easy. One of the giveaways to the forgery was Constantine’s apparent bequeathing of his own city to papal spiritual control. Although supposedly written in 315, Constantine did not in fact found Constantinople until 326, 11 years after his apparent donation.”
― Phil Mason, Napoleon's Hemorrhoids: ... and Other Small Events That Changed History