The earliest Christians were outcast and used the Ichthys fish symbol as a way to know if some one was Christian. This would prevent prosecution or death from the Romans. As Christianity became more popular over time, but made a huge expansion when the Roman Emperor Constantine claimed Christianity as his religion and thus the religion of the Roman Empire. Jerusalem is mostly important to Christianity because that is where Jesus Christ was brought to occasionally as a child, preached to the poor in his adult life, crucified in the end of his life, and resurrected by God. The Church of the Holy Sepulchre is said to have been built over the location where Jesus was crucified and where the tomb was buried.