Located between the Federation and the Uncharted Territories, Romulan space encompasses an area that is considerably larger than the Klingon Empire.

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Romulus and Remus
Citadel Station

Abraxas IX
Algeron III (destroyed)
Artaleirh
Carraya IV (prison colony)
Chaltok IV
Chetzia III
Constanthus
Denchar Penal Colony
Devoras
Invidia
Khazara
Nequencia
Terix II
Unroth III
Valldon
United Federation of Planets