Ancient artifacts of the Thran Empire are discovered on the continent of Terisiare, including many advanced machines of war. Two brothers, Urza and Mishra, discover a stone in the Caves of Koilos; but, when they disturb it, it splits in two—Mightstone and Weakstone—unleashing the evil of Phyrexia on Dominaria. The ancient machines of the Thran are employed in battle once again as the Brothers' War takes place, an epic war between Urza and Mishra for control of both halves of the stone. The war culminates in the Sylex Blast, plunging the world into the Ice Age.