Today in History—February 24: When the Church Invented Time Travel

In 1582 a pope rearranged time.

Thursday, October 4, would be followed by Friday, October 15, according to a papal bull issued on this day. It erased 10 days and changed the calendar for Catholic Europe.

We have Pope Gregory XIII to thank for creating the commission that developed what we now call the Gregorian calendar. The changes corrected errors left over from Julius Caesar’s eponymous calendar, created in 46 BCE. The Julian calendar assumed a year was 365.25 days long, but a solar year is actually 11 minutes shorter. Over centuries, those stray minutes added up to roughly 10 missing days.

The new calendar also refined leap years: Century years (e.g., 1600, 1700, 1800) would only get a leap day if they were divisible by 400, preventing the calendar from drifting out of sync. (This calendar isn’t perfect, but it’s closer, requiring an adjustment roughly every 3,300 years.)

Pope Gregory’s papal bull Inter gravissimas (“In the gravest concern”) fixed it all at once. Catholics praised it, but Protestants declared it the work of the Antichrist. That sounds dramatic now, but at the time it felt, to some, like the Church was trying to control time itself—the ultimate overreach of papal authority.

Catholic countries adopted the new calendar right away, whereas other countries took their time. England waited nearly two centuries to switch (bringing its American colony along). Other holdouts included Russia (1918), Greece (1923), and Turkey (1926). Saudi Arabia started using it for civil purposes in 2016.

Why did the Catholic Church care about the calendar? Since 325 the Church had carefully aligned Easter and other celebrations with points of the solar calendar. By 1545 the vernal equinox was arriving too soon. Skipping 10 days put that equinox back on March 21—thereby correcting the date of Easter, which is observed on the first Sunday following the first full moon after the equinox.

The mismatch was also causing problems for farmers and sailors, who relied on the calendar to keep planting, harvesting, and navigating in step with the seasons.

This calendar should keep us on track…until about 4909, anyway. Stay tuned for another papal bull.