Question: when did the crucifix become the symbol of christianity?
Answer: 4th century, in the 2nd century, the 4th century

During the first two centuries of Christianity , the cross was rare in Christian iconography , as it depicts a purposely painful and gruesome method of public execution and Christians were reluctant to use it . A symbol similar to the cross , the staurogram , was used to abbreviate the Greek word for cross in very early New Testament manuscripts such as P66 , P45 and P75 , almost like a nomen sacrum ( nomina sacra ) . The extensive adoption of the cross as Christian iconographic symbol arose from the 4th century .