The Debrune civilization was an ancient offshoot of the Vulcans which would later move on to Romulus and found the Romulan Star Empire.
Its existence is marked solely by their archaeological remains, which can be found on Barradas III, which was an outpost of the Debrune in the 4th century CE.
It is also quite likely that the planets of Dessica II, Calder II, Yadalla Prime, and Draken IV were also associated with the Debrune or other early Romulan dissidents. (TNG: "Gambit, Part I")