The Tkon Empire, a vast and technologically advanced civilisation, became extinct about 600,000 years before the 24th century, though some of its automated outposts survived.
The Tkon Empire was an interstellar power that flourished long before humanity existed and spread its influence across many star systems. According to Data, it became extinct about 600,000 years before the 24th century, and little remained of it beyond scattered ruins and machines.
In 2364 the Enterprise-D and a Ferengi ship were trapped by a power-draining field at Delphi Ardu IV, a former Tkon outpost. Riker confronted Portal, a guardian who still awaited the orders of his long-dead empire, and impressed him enough with a quotation from Sun Tzu that both ships were released.