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Steg, I don't want to ignore religious history, I find it fascinating.
As for grave and body decoration after death, we have no idea whether or not that had anything to do with what we would call religion. If my wife died in those days, I would not have chucked her in a ditch, I would have placed her reverently somewhere safe from predators, and given her a favourite dress or make-up. When someone died it would be natural to continue to respect the body and treat it accordingly. When a conqueror kills an enemy and mutilates and defiles the corpse, it's not done because of a belief in an afterlife.