Many Orthodox churches base their Easter date on the Julian calendar, which differs from the Gregorian calendar that is used by many western countries. Therefore the Orthodox Easter period often (but not always) occurs at a different date compared with the western Easter which falls after the March Equinox. There are different types of Orthodox churches including the Coptic Orthodox Church and the Greek Orthodox Church An important symbol of Easter is the Easter egg which is hard-boiled and dyed red to symbolize the blood of Christ. It is connected with spring fertility rituals in many early civilizations. Many Greek Orthodox Christians rap their eggs against their friends' eggs and the owner of the last uncracked egg is considered lucky. The Orthodox custom of decorating the round Easter bread with red eggs at the four edges of the cross on the bread dates back to around the 12th century. Another important symbol associated with Easter is the lamb. It is often depicted with a banner that bears a cross, and it is known as the Agnus Dei, meaning "Lamb of God" in Latin.