Actually, for almost any ancient discovery, it just understood that there may have been unrecorded
discoverers before the recorded ones. Since this is just understood,
it usually goes without saying.
Empirical evidence suggests the
Earth's surface is curved.
Since everywhere perpendicular to the surface is downward due to
gravity,
there may be a center of curvature and the known
Earth may be part of a
sphere.
As you move north
and south some
stars become
blocked or unblocked from sight by the Earth
just as if the Earth were curved.
If the sky
were a big dome over a
flat Earth,
why did no one seem ever get closer to the
point where the dome passed below the
flat Earth.
A spherical Earth explains this.
Another perspective on the same point is that the
horizon is always on average the
same distance away no matter where you are on
Earth.
It moves with you.
Again a spherical Earth explains this.