The Phantom Time Hypothesis is a historical conspiracy theory which suggests that a period of history, specifically A.D. 614 to 911, was fabricated or altered. This hypothesis was primarily advanced by Heribert Illig in 1991. According to Illig, historical events and figures from this period, including Charlemagne, were either misdated or invented. He proposes that the Gregorian calendar, the calendar system used by most of the world today, was manipulated to add these extra 297 years that never actually occurred.

Illig's theory is based on a few key arguments: the scarcity of archaeological evidence and written documents from this period, perceived inconsistencies in dating methods, and the supposed motivations of medieval rulers to alter the calendar. However, the Phantom Time Hypothesis is not supported by mainstream historians and is considered a fringe theory. It is widely rejected due to substantial historical, astronomical, and archaeological evidence that contradicts Illig's claims.