>>1011831Christianity was based on Judaism, which in turn was based on Paganism; the original reason the cross was considered sacred is because the Pagans associated the shape with the flower of various plants of a massive genus we now call 'Brassicas'. Given that finding nutrient-rich food in the wild tends to be pretty challenging, being able to recognize a plant you've never seen before as a Brassica just by the flower which is common across the genus, and therefore know that the plant is, in its entirety, edible, was certainly a thing worth worshiping.
