Christians around the world Sunday are celebrating Easter —
the day they believe Jesus arose from the dead. It is the holiest day of the Christian calendar.
Easter is Christianity's "moveable feast," falling on a different date each year. Western Christian churches celebrate Easter on the first Sunday following the full moon after the vernal equinox.
Thousands of the faithful gathered in the Vatican's Saint Peter's Square to hear Pope Francis deliver the annual "Urbi et Orbi" — "to the city and to the world" — Easter address.
Easter marks the end of Holy Week, which is the week before Easter and includes Maundy Thursday, the day of Jesus' last supper with his disciples. Holy Week also includes Good Friday, the day Jesus was crucified.
The Eastern Orthodox church celebrates Easter next Sunday, April 8.
The two Easters are usually weeks apart with the Western Christian church following the Gregorian calendar, while the Eastern Orthodox uses the older Julian calendar. Last year, however, Easter was celebrated on the same day in both traditions.