Romulan flagship
The Romulan flagship was a type of warship that was in service with the military of the Romulan Star Empire during the latter half of the 23rd century under personal command of the Romulan Praetor.

History

In an alternate timeline where Captain Christopher Pike remained in command of the Enterprise and avoided the accident that exposed him to delta radiation, the Praetor responded to a message sent out by Romulan sub-commander Deciusafter their Romulan Bird-of-Prey attacked and destroyed Earth Outpost 4. After the Enterprise transmitted recorded footage of the Bird-of-Prey destroying the outpost, the Praetor's vessel opened fire, and destroyed the offending Bird-of-Prey, for getting caught. 

A few moments later, the Praetor's flagship, and its fleet, opened fire on the Enterprise, declaring war against the United Federation of Planets, after repeated attempts at diplomacy from Pike were interpreted as a sign of weakness. 

The war dragged out for years, resulting in millions dead. ()