The Romulans, cousins to the Vulcans, were first encountered around 2160 when bitter wars raged between Earth forces and Romulans. At the conclusion of these wars the Romulan Neutral Zone, a one light-year wide strip of space, was enacted as a neutral buffer between Romulan and Earth space. In accordance with the Treaty of Algeron any penetration of this barrier was considered an act of war. The Zone remained un-violated until 2266 when a single Romulan ship entered the Neutral Zone to test Federation resolve. This penetration caused tension along the border which has remained to the present.
This D'deridex class Romulan warbird was first encountered in 2364 by the Enterprise when the Romulans violated the Romulan Neutral Zone. Nearly twice the length of the Enterprise (approx. 1282 m.) and with more firepower, this craft a large powerful battle fortress. It uses an artificial quantum singularity to power its warp-drive which has a maximum speed of 9.6 although it is believed it cannot maintain this speed as long as the Enterprise.