Slaughter at Bleak Meadow

The Slaughter at Bleak Meadow was a major battle in XI, 90, within which the High Elves came to the aid of the Wood Elves against the Beastmen hordes.

When word reached Ulthuan that Athel Loren was beset by a Beastman warherd of unparalleled size and ferocity, the Phoenix King saw an opportunity to ease the trouble relationship between the two kingdoms. Swiftly, an army was assembled and took ship overseas, their aim to bring aid to their estranged kin. Thus were the beastmen caught between the wrath of two Elf realms.

Little trust was there between the Elves of the forest and the warriors of the Phoenix King, but mutual loathing of the Beastmen soon overcame all reserve. Eternal Guard locked shields with the spearmen of Cothique, and Sapherian wizards blunted Chaos magics whilst Spellsingers roused the living forest. At the heart of the battle, Scarloc of Loren and Ystranna of Avelorn fought back-to-back, bowstrings blurring as their arrows scythed through ranks of Bestigors. Come the dawn, the warherd had been destroyed. The Elven armies went their separate ways, each having earned fresh respect for the other.

Source
pg. 28
 * Warhammer Armies: High Elves (8th Edition)