On the Field of Ruins — around the Saerun Road in the southwest part of the Mournland, where allied forces of Thrane and Breland battled an outnumbered Cyran army on the Day of Mourning — the fallen soldiers are preserved just as they fell, with no sign of rot or decay. Thousands upon thousands of corpses lie scattered across the field, facedown in the dirt or staring lifelessly at the gray sky. Even seasoned bands of treasure hunters are loath to enter the Field of Ruins.
Source: Rising from the Last War
Nowhere else is Cyre’s status as an open grave more apparent than on the last battlefield of the Last War. The base camps of the armies fighting on the Day of Mourning can still be seen, their tents and watchtowers creaking in the forlorn wind. Clockwise from the north, they include a hastily assembled Thrane shrine to the Silver Flame, the crude cabins and workshops of the main encampment of the Western Army of Cyre, the ditches and palisades of Darguun armies who had been fighting in the area for over a year, and the newly established base of the Brelish warforged hero Bastion, who had arrived with a major force of humans and gnomes only weeks earlier. In the fields between these hastily built towns, tens of thousands of troops and war machines were committed in a battle that held the destiny of Cyre and likely the outcome of the Last War as the prize. The outcome was far different from what anyone expected.
Today, a large cliff divides the once smooth plain into eastern and western halves. Part of the uprising that formed the Glass Plateau, the ground burst open so suddenly that warriors fighting at sword’s reach found themselves abruptly separated by a 100-foot drop—moments before the arcane energies took their lives. The fiercest fighting took place along an old trade road from Lyrenton to Making, which still cuts across the fields above the cliff line, becoming more patchy and broken until it vanishes into the Glass Plateau. Even seasoned groups of treasure hunters enter the battlefield with extra caution. The sight of the thousands of dead warriors has placed a hint of respect into the hearts of even the most craven of grave robbers.
Source: Five Nations
Allied armies from Breland and Thrane—supported by mercenaries from Zilargo, Valenar, and Darguun— converged in this broad area to do battle with the Cyran army. Along the Saerun Road, they clashed in what might have been a decisive battle. As it turned out, this was the final major military event in the Last War. Soldiers on all sides—tens of thousands of them— died here in the Mourning. This haunted place is now the largest open grave in Eberron.
Not one item or corpse here shows any sign of decay or predation. The unwounded look as if they are sleeping, and weapons unmarred by time and weather shine in the Mournland’s eerie half-light. War machines and military encampments stand idle, silent except when the wind moans and the wood creaks.
A large cliff now divides what was once rolling plains. It breaks the Saerun Road, which continues east toward Making before disappearing on the Glass Plateau. Since the fighting was fiercest between units vying for control of the road, the bodies and hazards are also thickest along it.
Source: Eberron Campaign Guide
The last battle of the Last War took place in Cyre southwest of what is now the Glass Plateau. Here, forces from Thrane, Cyre, Breland, and Darguun clashed in a chaotic epic battle. Those forces died on the Day of Mourning, caught in the backlash of the arcane effect that destroyed the entire nation. The remains of this battle can still be seen; the Field of Ruins is noteworthy among similar places throughout the Mournland primarily because of the sheer number of troops whose bodies litter this battlefield. These soldiers, who died four years ago, appear as they did the day life abandoned them. Not one has shown signs of rot or decay. Wounds gape wide, flesh refuses to fester and flake, armor and weapons remain untarnished and rust-free. Vast war machines, siege engines, and other devices of destruction brought by the opposing forces now stand in silent vigil over the bodies of the dead.
Most visitors to the Field of Ruins find themselves moved to follow the example of the explorer who discovered the place, offering prayers to all those who sprawl in this uncovered grave—Thrane knights lying beside Darguun warriors, Brelish archers piled among Cyran militia. They are not undead, but they are unnatural just the same, for some force keeps them preserved despite the passage of time. Even the scavenging beasts of the Mournland refuse to disturb these bodies.
Source: Eberron Campaign Setting