Shindolay is not a land without dangers, and those who dwell there are not unskilled in the fashioning of arms and weapons. Beasts stalk the deeps and dwell in the river bottoms. But more than that the Void looks upon Shindolay and there is no Wall of Worlds to keep out the horrors that dwell in that Empty place. Only the sorcery of the elves.
Elven sorcerers had long since discovered the world of Aihrde and the other dimensions and planes. They spoke of these far flung realms, attempted to study them. Some few, very powerful wizards, could cross over to them. But few of these returned and those that did were affected in some way and always sought to cross the divides again, either that, or they withered away.
When the All Father passed from the Arc of Time, the Land of Seven Rivers fell into, or joined, the world of Aihrde and the elves were free to cross over into the world. Many did so, mostly people from the Pth, Ra and Uul and they came first to the great forest Rond in the east, beyond the Marl. But there were members of all the tribes that crossed over and they mingled together for they entered the strange lands and dimensions without friend and many foes.
~ Players Guide to Aihrde