We know that the realm of sapience and its surrounding waters are
quite large. In fact I would estimate that it would be at least
several hundred miles from shore to shore. Now of course this is
not including the ocean, which stretches as far as the eye can
see in every direction.

Now let us suppose you're theory is correct and there is a rim to
achaea, and the world is flat.

In a short time speaking with an alchemist named Newton (famous
for his work in later years in alchemy) I have discovered that all
object exhert a force he call gravity. And it is this force which
keeps us on the ground. Now gravity radiates out from an object,
the bigger the object the stronger the pull of the gravity. Since
we can safely assume that achaea covers at least 600 square miles,
and extends at least 2-3 miles below the surface of the ground, we
can say that there is around 1800 cubic miles of rock on achaea.

I'm going to underestimate the weight of a single cubic mile of rock
to be around 1000 tons. meaning Achaea has at least an approximate
total mass of one million, eight hundred thousand tons.

This much mass spread out into a flat surface would exhert such an
amazing amount of force upon its edges that eventually the shape
would collapse in upon itself. If you would truly like me to I
could provide you with the actual numbers. However since Achaea
hasn't collapsed in upon itself, and still stretches for miles in
every direction, we can safely assume we only see a small portion
of a much larger globe. Especially since the shape of the globe
would be able to withstand such immense gravitational pressures.

-Dream, mathamatician for a day.

Penned by my hand on the 16th of Scarlatan, in the year 245 AF.