The Battlefield of Sorrow

During the ongoing Saxon Wars many skirmishes & battles have took place. With no end in sight, the carage that has been experienced on both sides have led to many combatants suffering mentally afterwards.
One notorious battle led to a collapse of both armies. A Frankish army had marched as far as a plain a few miles north of Heidelberg looking to assault the city in the summer of 795 AD. They were spied upon by scouts of the Saxons that controlled the city and swiftly reported back.
Within an hour the Saxons had assembled what troops they could and sallied forth to the edge of the plain where they soon met & vlashed with the Franks. Taking heavy damage from the Frankish cavalry, the Saxons threw caution to the wind and charged en mass towards the Frankish lines.
Slamming into the Franks like this led to difficulty for the latter's cavalry to get a good charge in against the Saxons. The Saxons themselves used magic to bolster their weakened lines and to try to disrupt the Frankish units. Along with this and the savagery of the fighting it caused an effect like nothing before or since.
A tear appeared above the battlefield and water gushed through at such force it threatened to drown a good number of men. Not just any kind of water but a cold fetid stinking rush of water that smellled of the grave. It was acommpanied with a wind that sounjded distinctly like the wailing & crying of women & children. This caused the remaining warriors on both sides to stop in wonder, and then near all sheathed or dropped their weapons.
A despondency set in to all of them. It was as if the afterlife or the underworld had opened up and spilled the waters of these places out to show the agony of those left behind after the warriors had butchered each other. Each one, standing there soaked and sinking up to their ankles in the waterlogged ground, felt despair like they never felt before. The feeling of what is the point of continuing this sunk in.
Both sides collected their dead & equipment and trudged off the battlefield at this point, wondering still what had happened. They returned to their sides telling their superiors what had happened and the effect it had. None of them wanted to take up arms again, but grudgingly did, keeping it to themselves under penalty of death for cowardice & desertation if they spoke about it ever again.
What they didn't know, lying beneath the groud was an old primitive temple, covered over by centures of dirt and plant life. It had shrines to many dfifferent gods made of wood, animal skins & bones, and ancestor burials of the long forgotten builders. The temple itself was used to worship nature, both good & evil, life & death, birth, death and rebirth. It also had a substance at it's core, used by many ancient peoples to commune with gods long forgotten.
When the carnage & magic was unleashed above, it stirred back to life calling out to these forgotten gods. The magic opened a link between these gods world and the Material Plane while the souls of the dead were collected & consumed. They stir there now in the old temple looking for others to come, and to take their fill. After a time they will heal the land as they see fit and bring worshippers to themselves.
The only clue to this is a statue carved out of mammoth tusk lying in a protected vault of the Saxon overlords of Heidelberg. It depictes two figures, one with wings & one with horns, fighting each other with fists & what appears to be water up to their knees. Unknown script is carved around the base.