The Grey Mountains
The Grey Mountains are a 6000 mile long mountain chain that extends from the Crimson Ocean coast separating Makael from Xicomor, north and northwest until they reach the cold polar shores of the Great Northern Sea. As such, it divides the continent of Invinni into two unequal portions. The Grey Mountains also form the western borders of Ghananda and Celobsil. For most of their length they are passable, save for a thousand mile long section that borders Ghananda, northern Makael and Celobsil, where nothing can cross them.
They have been effective at both preventing Aesedran expansion westward, and most major incursions into Aesedra from the west.