Dahl is a district of Trantor.
Hari Seldon first encountered it during the event known as The Flight. It is a small and rather down-trodden sector, which does not necessarily seem politically ambitious. Dahlites, as the residents of the sector are called, have a mythical belief that they come from the original single planet inhabited by humans.
Dahlite men have a tendency to wear thick, black mustaches, which they prize as they do their honor. Despite the ban on illegal weapons in all of Trantor, most Dahlites carry knives are are adept at using them.
One of the many prominent features of Dahl are its heat-sinks, which are an important source of energy for the empire. An entire class of Dahlites, called heat-sinkers, work underground near these heat sinks, and are often shunned by higher-class Dahlites as inferior. Yugo Amaryl, who was perhaps the second most important person in the development of psychohistory, was a heat-sinker on Dahl before meeting Hari Seldon during the latter's flight from the Emperor Cleon I.