Item from Fourth Wing by Rebecca Yarros
Massive magical stones that power Navarre's protective wards — ancient, irreplaceable, and being drained by the venin faster than anyone will admit. The real war is about these.
Wardstones are the physical anchors of Navarre's magical defenses. These massive stones, placed at strategic points across the kingdom, generate the Wards that keep venin and wyverns from crossing the border. Each stone is ancient and irreplaceable — the knowledge to create new ones has been lost. The venin actively target wardstones, draining their power to fuel their own dark magic. As wardstones fail, gaps appear in the Wards, and creatures that Navarre's people have never had to face begin slipping through. The wardstones are the series' central MacGuffin: whoever controls them controls the fate of the continent.