Showing the pagan religious origin of the cross, the book The Ancient Church by clergyman W. D. Killen says (1859 edition, page 316):
“From the most remote antiquity the cross was venerated in Egypt and Syria; it was held in equal honour by the Buddhists of the East; . . . about the commencement of our era, the pagans were wont to make the sign of a cross upon the forehead in the celebration of some of their sacred mysteries.”
The Truth That Leads to Eternal Life. 1968, 1981 ed. p. 141-142