Tractis was the homeworld of the Tractites. Its capital city was Noctutis and Tafalis was another city on the planet. Some time after the 26th century, the Earth Empire invaded Tractis and enslaved and killed the Tractites.
Some of them escaped. These used a Time Tree to time travel into Earth's history and alter it so that the human race never evolved. This alternate Earth was called "Para-tractis". (PROSE: Genocide)