For those unfamiliar with Eberron, the setting takes place in the aftermath of the Last War, a great war between five nations which lasted over a century. One of those nations, Cyre, was completely wiped out in an unprecedented and unexplained event known as The Mourning.

All along the borders of Cyre– political borders, mind you, not just natural borders– there is a wall of mist. Within, time seems frozen, as the land is littered with the corpses of those killed in the Mourning, but still appearing as fresh as to have just died that day.

Here are three possible explanations for the Day of Mourning to provide inspiration and possibilities.

Sacrificed for the good of all

It is a fact that the catastrophic event which destroyed Cyre spurred the remaining four nations into signing the Treaty of Thronehold and ending the generations-long Last War. Perhaps this was exactly why Cyre was destroyed. Someone or something with the knowledge and power to do so destroyed Cyre as a way to end the war once and for all.

Who could have done such a thing, and how? Why Cyre? Is the culprit still alive and present on Eberron? Perhaps they even had a hand in the Treaty of Thronehold itself.

Variation

The players get the opportunity to change history through time travel, a wish, or something similar, and stop the Day of Mourning from ever happening. Should they do so, they find the world changed and themselves entrenched in a war that never ended.

Exodus

Cyre was not, in fact, destroyed. Rather, a plot was discovered among the other four nations to destroy Cyre once and for all. On the very day the combined strike was to happen, Cannith magewrights loyal to Cyre managed to shift the entire country into a demiplane in Siberys, leaving the shattered crater which is the Mournlands in its wake.

The reason the Cyran ruins and bodies of those present remain is due to the nature of the act. It wasn’t a true planeshift, but more like a cloning of the country into the demiplane. This cloning took place over several weeks, and when it was complete the final step was taken, transferring the essence of all life from the old Cyre to the new. In fact, the other countries’ combined attack was necessary for this plan to work, as it required the added lifeforce of the foreign soldiers.

The players could discover this piece by piece, first learning of the impending attack on the same day, then discovering the Cyran government knew of the attack and had begun a plan to escape it. In the end, the players might visit the living Cyre.

Variation

The plan was not successful. The attempt to transfer the country to the demiplane was sabotaged, aborted midway, or perhaps never even fully conceived in the first place. Regardless, Cyre exists now trapped halfway within Eberron and halfway within Siberys. If the PCs could find some way to undo the transfer, Cyre could be restored to a normal, if devastated, state and re-colonized.

Scrubbed from Reality

This Eberron is but one of many existing in parallel realities. In another, the Last War ended considerably earlier, with a magically-advanged Cyre dominating the other four countries and eventually the world. The Cyran rulers were cruel and harsh, and when the others finally managed to overthrow Cyre a plan of ultimate revenge was concocted.

The others used the Cyran magic against the country, destroying not only their former oppressor but also every copy of it in every other reality.

The PCs might stumble upon something odd along the edge of the mournlands, a bit where it extends beyond Cyre’s borders, or even a bit of Cyre which is untouched. After performing some research, the PCs discover that the affected land was once offered to Cyre as part of a rejected negotiation, or Cyre had gained the unaffected land through something similar.

The key is that in the alternate reality, these changes didn’t take place and the Mourning followed the border of that reality’s Cyre. If the PCs put two and two together, they might even be able to visit some of the alternate realities and see what might have been.