Mediterranean countries had artificial candle-or-whatever light with which to play upon spherical fruit dangling from trees, which otherwise in the daytime caught specular light glimmering through leaves.
Knowing the Earth was round, I don't find it hard to imagine that interested minds of the day picked a fruit and toyed with it in hand, squinting a bit and considering the implications.
True, and surely some did—not just in the Mediterranean but in Perú and in Punt, and not just 2500 years ago but even a quarter million years ago—but, despite the whole lunar-eclipse thing, nobody had a really compelling argument until Eratosthenes precisely measured its curvature.
That is, though the wise could imagine a spherical Earth for as long as they have had fruit, they could just as easily imagine a non-spherical Earth. More easily, I think, because, I mean, look around you, it looks flat. It wasn't until Eratosthenes that the wise lost the ability to believe that the Earth was flat.
Knowing the Earth was round, I don't find it hard to imagine that interested minds of the day picked a fruit and toyed with it in hand, squinting a bit and considering the implications.