The Calamity

In the year 1000 AM, a great force of destruction left waste to the eastern continent of Eanefell, known as The Calamity. It rose from the crater in the center of the continent, decimating anything in it's path, shattering the ground and dispelling all life within it's area, traveling throughout and destroying most life and civilization of Eanefell.
The Calamity was a gargantuan creature, unlike any seen before, the size of a small city, crushing villages with a single step. It's impenetrable shell fended off the Dragons which attacked from above, being forced to retreat by the spike like missiles that were being hurtled from the shell. With it's own powerful magical aura, it seemed immune to all spells thrown at it, all he people on the continent could do was move out of it's path and let it destroy.
It did not come alone however, smaller creatures, less powerful, followed from the crater, roaming the lands and causing havoc on a smaller scale. These creatures are still around, even after The Calamity was sealed, still numbering in the thousands with seemingly no end. However, that may not be an entirely bad thing as the Dragonborn on Eanefell now use their hearts as a valuable recourse.
Fifty years after The Calamity rose from the ground, it was sealed away by The Heroes in an unmarked location, allowing the now Shattered Planes and Bubbling Wastes to be free from it's terror, and begin recovering from it's destruction.