Ancient astronomers thought that earth was flat. which observation eventually proved that this is wrong?

While it is a common belief to people in the ancient civilisations that the Earth is considered as "flat", the contrary idea that the Earth could be considered as "spherical" was first theorised by the famous ancient philosopher Aristotle when he observed that a circular shadow was cast by the moon during a lunar eclipse.

Ibelieve is d but i’m not 100% sure