Kasteroborous was a galaxy. In the Alpha and Beta Quadrants of the Milky Way Galaxy, there were legends of a civilization in the Kasteroborous galaxy that developed and mastered time travel. However, they found the risks of time traveling and interfering in the time-lines to be so unpredictable and dangerous that they never dared do anything at all, and stagnated. Captain James T. Kirk considered these legends when contemplating the effects of Klingons time-traveling to 19th century Earth from 2267 (TOS novel: Ishmael).