The Battles of Nyan Marmu

The Battles of Nyan Marmu were a protracted series of sieges with the aim of destroying the last Eldar and subduing all of Plethira.

Sieges
The first siege ended in failure, as the Keth failed to breach the walls. The Eldar, meanwhile, amassed the Weapons of Light, as the sieges continued and failed. Eventually, led by Cil-Ajura, son of Cil-Nuhûtis, they went on the offensive and destroyed the Horde.

Aftermath
The defeat of the Horde, although it at first seemed catastrophic, was minuscule for the Dark God. The Eldar summoned every last one of their kind, women as well, and joined with the Celestials and Mannish hosts to march north.