The world is flat.
Explorers have proved the fact countless times, as has the Grox Royal navy when, through use of its highly skilled storm mages, it drove the Selexian navy off the edge of the world. It was a great triumph, and that victory made possible the Grand Union of Humanoid Nations. The Grand Union, or Gruhn as it is sometimes called, was the height of expansion, glory and knowledge of the mortal races. It stretched from the western edge of the world to the eastern most point of the Indoldian islands. That was 200 years ago; things have changed since then…
100 years after the Grand Union brought the Tirstoc Continent together disaster struck. From the east flew mighty armies, The Great Host, enormous sky ships pulled by dragons carried hordes of Giants, Titans, and Elementals. They swept across Tirstoc with little resistance, and smashed or burned every remnant of the Grand Union or its holdings on the continent. Then, just as they had pushed the remaining people to the edge of the world, as the western sea was the only thing remaining for the Gruhn Army to pull back to, they stopped. No one knows why.
The past 100 years have been troubling; every incursion deeper into Tirstoc has been met with devastating losses. The land that was once the Grand Union’s vast empire has been reclaimed by the beasts of the world, or reclaimed by the land itself. But The Grand Union remains, pressed against the edge of the world, humanoids of all races work together for survival, the only other option is a short swim and a long fall.