Thousands gather at Colosseum to celebrate the way of the cross

Catholics, Protestants and Orthodox Christians on Sunday will celebrate Easter, the most important holiday in the Christian calendar, which commemorates Christ's death and his believed resurrection through centuries-old traditions. 

The date of Easter is not fixed, as it is celebrated on the first Sunday following the spring full moon. It follows Lent, a 40-day period of fasting and prayer in reference to Jesus's time in the desert. Holy Week kicked off with Palm Sunday, commemorating Jesus's entry into Jerusalem nearly 2,000 years ago for the Jewish Passover celebrations.

Catholics and Protestants celebrate Easter on the same day because they follow the Gregorian calendar, unlike the Orthodox Church, which follows the Julian calendar. This year, the two calendars coincide -- a rare coincidence.