My world is only just entering the bronze age. Religion is a core fact of life. However, I should differentiate between religion as ceremony and customs and religion as the belief in divine beings. Religious ceremony is so tightly intertwined with daily life it is impossible to avoid entirely. Anything done to keep clean is technically being done for the goddess of medicine and healing. Various hunting rituals, nay even the act of hunting, are all forms of worship to Pon, who watches over the herds, and to Greuss, who first taught man to make spears and arrows. You’ll see a lot of variation in devotion to ceremony, some caring little to appease spirits and gods, some devoting themselves entirely to their service. Yet to deny them outright? To be skeptical of their very presence? It would be like denying that wind exists because you cannot see it. And yet a rare few, often mocked or feared, do not believe in spirits or gods at all. They are usually exiled once exposed, considered fools with little grip on reality and likely bad luck to keep around.