"Among its [Hinduism] direct roots is the historical Vedic religion of Iron Age India. As such, Hinduism is often called the 'oldest religion' or 'oldest living religion' in the world." - Wikipedia,(Merriam-Webster's Collegiate Encyclopedia)<quoted text>
OK, here you are pulling the proverbial shyte out of your azz...'It's thought to be"... gee, did you pull that one from the EVO playbook?
Interesting as you state 'culture', yet Christianity is not set to one culture, but hundreds if not thousands...
Christianity was the official religion of the Roman Empire (Western Culture) for 1,500 years. It may have existed in other cultures as did Judaism but only in small numbers.