The Corillian Incident was a short war between the Romulan Star Empire and the Corillian civilization.
The conflict started on reference stardate -1/0401 when the previously unknown Corillians attacked from a spinward position into Romulan space. Having little force in that area, the Romulans sustained heavy casualties with the war lasting six months. However, as the Stellar Kingdom of Corill were a much smaller culture, they were quickly conquered by the Romulans and became one of the first spacefaring cultures assimilated into the growing Romulan Empire. (FASA RPG module: The Romulan Way: Game Operations Manual)
Commander Arenius Triario was noted as being a famous Romulan fleet officer during the conflict, a command officer who led a confrontation against the Corillian fleet and defeated them. (FASA RPG module: Romulan Ship Recognition Manual)
Between stardates -1/0600 to -1/8600, the Corillian Incident made the Romulans realize the necessity in watching their space from all directions and not just focus on the coreward main expansion. This led to a period of consolidation while the Empire began strengthening their existing borders. (FASA RPG - The Romulans module: The Romulan Way: Game Operations Manual)