What is known
"The Enemy was unstoppable. Waves of chaos spawn rolled over the continent, killing the lucky and 'absorbing' those unlucky enough to survive.
The older races: the Elves and the Dwarves sealed themselves off from the world and left the younger races to their fate. The Elves watched from within their eldritch forests as the world burned and millions died, but found only inspiration for their art, prose for their poetry, and new songs from the screams of a dying world. The dwarves sealed themselves inside their cyclopean mountain fortresses, abandoning a surface world that had rarely held their interest for long.
The deceptive Goblins and the bloody-minded Orcs found common cause at last with their perennial enemies the Humans, who were unmatched by either in the arts of deception and bloodshed. These former enemies slowed the advance, but only long enough for their people to continue the slow retreat westward.
As the masses ran, and the soldiers fought, sorcerers schemed. The necromantic lore of the Magus Anima school, long forbidden, were thrust to the fore of the fight. Tens of thousands who had already died in the losing war were called to duty again... and again to stem the tide of the Enemy's advance.
It was only a matter of time before the younger races would find their backs to the sea, unable to retreat any further. A new path needed to be found.
It had long been known that this was not the only world, that in fact each world had a near infinite number of near 'copies' of itself throughout creation. Indeed the Enemy was not native to this world but had crossed over... and continued to crossover in a manner that had baffled sorcerers until recently.
Unfortunately it was too late to close this portal as this world was lost. A portal could be opened to another world however, and this was the last hope for the younger races to survive.
Time was running short, and the sorceries involved were maddeningly complex and the price to crossover would be high. Passage through the portal was one way, so there was no telling what was on the other side, and the price of passage was steep: for every living being that passed through, one would be taken by the portal as a sacrifice. Who or what would be sacrificed was seemingly random, and meant that the cost of sending a horse through the portal could be the life of a lover, a sibling or a child.
Hard choices are easy to make, when there is but one. To start life anew meant that agricultural animals would take a priority over anything else. What need do you have of a cobbler or a soldier if you have no food to feed him as you have no plough-horse to till your fields?
Some way was needed to slow the advance of the Enemy for as long as possible to allow as many as possible to flee through the gate. The Human Necromancers had a plan: use their necromantic arts to subvert the living defences of the Elven forests. The Elves dispassionate amusement at the plight of the younger races quickly turned to terror as their undying bodies gave endless amusement to the ravaging mouths and claws of the Enemy, their newfound torment providing the time needed for thousands more to escape.
The most powerful heroes and villains of the age would form a final wall of defense. When the Enemy began to advance again, this Legion would hold them as long as possible to allow the remaining sorcerers to close the portal, so as to prevent the enemy from following the Exodus to the new world.
The sacrifices of this Legion are unknown, each soldier and each sorcerer died with no historian to record their names, and no bards to sing of their deeds."