re: When did the idea that we're all "created equally" become a widely held belief?

quote:

---

If you call yourself Christian,...That would've been about two thousand years ago.

---

This.

The OP question asks about a belief. They also use quotes to reference to an idea ("created equally"), which I think implies an allowance for some latitude in interpretation of that term.

All that said, I think this belief has become most widely held since the advent of Christianity, as JudgeHolden stated.

The recorded teachings of Jesus posit that we are all loved equally in the eyes of God - so it follows that we are all equal in the eyes of God. For believers, you can't get more equal than that.