Waystones

Waystones are towering rune-carved menhirs that channel and redirect the Winds of Magic. Each waystone collects the raw power of Chaos and directs it to an inward neighbour. Thus are the magical energies of the world inexorably drawn, like the waters of a whirlpool, to Ulthuan's heart. There the magic is drained from the world by the Great Vortex. 9

For the High Elves, there is also a secondary purpose. It is said that, to hungry gods, Elven spirit stuff is the most delectable of all prizes. Slaanesh, the Dark Prince of Chaos, is rapacious in all his appetites, but thirsts for Elven souls beyond all others. Those few who escape his maw must then evade the grasp of Ereth Khial, the Pale Queen. Such fates are truly worse than death, ending either in total obliteration of the soul, or torment without end.

To guard against this, all High Elves are spiritually bound to the waystones of their ancestral lands. From the moment of binding onwards, each Elf feels a powerful connection to the land upon which his waystone rests, though he may spend a lifetime wandering other lands. Many High Elves carry wayshards, small gemstones attuned to the network of waystones that allow their bearers to 'feel' the position of individual stones, and thus navigate the world.

When an Elf dies, his soul is drawn to his bound waystone, and becomes part of the ritual that sustains the Great Vortex. In this way, the folk of Ulthuan continue to protect, in death, the world they defended in life. It is even said that, at midnight, the hills and fields about a waystone tremble to the gallop of invisible hooves and ring with the din of a battle that lies beyond mortal sight.

Thus is the loss of even a single waystone a terrible tragedy. Not only does its fall diminish the magics of the Great Vortex, but with its destruction, the spirits within lose their anchor, and are left defenceless before the gaze of predatory gods.

Source

 * Warhammer Armies: High Elves (8th Edition) -- pg. 9, 26