When did Earth’s roundness become common knowledge?

[Rigamarole]

@panache45

The ancient Greeks knew that the earth is round. I think it was Aristotle who remarked that the earth casts a round shadow on the moon during a lunar eclipse. This was confirmed by astronomers in the third century BC. Don’t know whether the average Greek would have agreed.

But that doesn’t really preclude it from being perceived as a flat, round circle rather than a sphere that’s rotating.

ETA: nitpicky annoyance - “round” is not the appropriate word to use in this discussion, since circles are round. The OP is asking about when people knew that the Earth was (roughly) spherical.