It was on this day (July 16) in 622 that a new era in human history began. The date, which represents the first day of the first year on the Muslim calendar, marks the founding of what has become the world’s second-largest religion. It’s keyed to the historic event known as the Hegira, the flight of the Prophet Mohammad and his followers from a hostile Mecca to the more welcoming Medina. Credited with establishing the Islamic calendar is the faith’s second caliph, Umar I. He did so in the year 639 on what was known to Christian Europe as the Julian calendar. (In 1582, Europeans began using the reformed Gregorian calendar, which is now the world’s civil standard.) Confusion was inevitable. While Europeans were using a solar calendar with a 365¼-day year, the Middle East was marking time on a lunar calendar of either 354- or 355-day years. This year on September 21, the Muslim faithful will ring in the year 1439. As if we don’t have enough trouble understanding one another, do the math and it appears that those who adhere to Islam’s calendar either age faster or live longer than those who don’t. In the late 1970s, Syrian-born American filmmaker Moustapha Akkad discovered that understanding (in the form of tolerance) was in short supply when he set out to tell the story of his faith’s founding. Protests and a Washington D.C. hostage crisis followed the release of 1976’s Mohammad, Messenger of God.