Cross culture

Many people believe cross means Christianity. How come it came to be a symbol of Christianity?

Jesus was believed to be crucified on the cross, that is one reason. The fish mark was used to represent Christ, and cross might be the simplified form for fish or Christ. The first Greek letter for Christ is X as the abbreviation form Xmas suggests and X became the representation for Christianity. Cross had been used to represent Seraph, or angel, cross came to represent Christ after people started believing Christ became angel after resurrection.

In Japan there's very few church and many people here don't know the relationship of cross and Christianity. For almost all people here cross is just a decoration of some design. Probably I think cross was used to indicate an important target as a bull's eye, this could have meant simply an objective of life.