Thran

the long version

"Before planeswalkers, before the five colors of magic, before history itself, the plane of Dominaria was ruled by the Thran. They built machines and artifacts, the likes of which have never since been seen. But amid this civilization, a shadow took root, one that would stretch its arms across space and time: the hideous evil of Phyrexia was born. And in its wake arose a mighty conflict between the brothers Urza and Mishra, a battle of titanic engines that scarred an entire plane and that altered the course of history. So begins the saga of the brothers' war"--P. [4] of cover.