The cross did not become popular as a symbol in Christendom until the fourth century C.E., when Roman emperor Constantine adopted the labarum, a flag bearing the symbol [Artwork​—Greek character]. However, this represented, not Jesus’ death stake, but the Greek letters khi (X) and hro (P) one atop the other. Many began to view this symbol as depicting the first two letters of the Greek word for Christ (XRistos).a

“Crosses were used as symbols of the Babylonian sun-god, [Artwork​—Symbol], and are first seen on a coin of Julius Caesar. 100-44 B.C., and then on a coin struck by Caesar’s heir (Augustus), 20 B.C. On the coins of Constantine the most frequent symbol is [Artwork​—Greek character]; but the same symbol is used without the surrounding circle, and with the four equal arms vertical and horizontal; and this was the symbol specially venerated as the ‘Solar Wheel’. It should be stated that Constantine was a sun-god worshipper, and would not enter the ‘Church’ till some quarter of a century after his having seen such a cross in the heavens. . . . The Lord was put to death upon an upright stake, and not on two pieces of timber placed at any angle.”