The Assiti were a sophisticated and curious alien race that mastered spacetime, which they used in making "art". However, their amusement and practice in their "artwork" was dangerous. For example, a minor mistake by the Assiti caused the transportation of the West Virginian town of Grantville and its inhabitants to the midst of 17th-century Europe during the Thirty Years' War, creating a whole new universe. Several of the Assiti Shards have hit Earth, resulting in multiple temporal transpositions and divergent timelines.