Christians, Jews, and Muslims celebrated an unusually holy weekend, as major holidays for the three religions fell on the same weekend, an intersection that only occurs every 30 years or so.

For Western Christians, Holy Week began on April 10 with Palm Sunday, the celebration of Jesus Christ’s entry into Jerusalem, and continued with Maundy Thursday — the celebration of Christ’s institution of the Eucharist —followed by Good Friday, which commemorates his crucifixion, and the celebration of his resurrection on Easter Sunday.

Following the method laid out at the 4th-century Council of Nicaea, Christians celebrate Easter on the first Sunday after the first full moon after the spring equinox.

Eastern Christians who still use the Julian calendar to determine the date of Easter observed Palm Sunday while their Western brethren were celebrating the resurrection.

For Jews, Saturday — extending from sundown on Friday to sundown on Saturday — marked the feast of Pesach, or “Passover,” which celebrates Israel’s ancient exodus from slavery in Egypt. Whereas the Christian calendar depends on the solar equinox, the date of Passover is determined by the lunar calendar, albeit with a complicated corrective process to ensure that the 354-day lunar years don’t cause Passover to drift out of spring, Robinson Meyer explains in The Atlantic.

Easter and Passover fall on the same weekend 16 years out of every 19, but the two only coincide with the Islamic holy month of Ramadan about once every 30 years. This is because Ramadan, which commemorates the revelation of the Quran to Muhammad, is based on an uncorrected lunar calendar and begins when observers in the Middle East literally see the crescent moon for the first time. For this reason, Deutsche Welle explains, Ramadan “moves across the Western calendar over the course of a good three decades.” Just 10 years ago, Ramadan began in late July.