Eternal War

The Time Lord-Vampire War was a protracted and extremely bloody conflict fought early in the history of the Time Lords, against the Great Vampires.

History
The war took on the status of a legend throughout most of the universe, with few exact details known. The origins of the Great Vampires were unknown, as was the precise reason for the conflict between them and Gallifrey.

According to a transmission which Samantha Jones received on Anathema (and which may have been influenced by Faction Paradox propaganda), the war began when Rassilon first opened a black hole, attempting to draw power from other planes of existence. This first attempt was relatively crude, and took place before Omega developed the stellar manipulator. The black hole reached through to an inhabited plane, and the Great Vampires swarmed through the opening Rassilon and Omega had created. (EDA: Interference - Book One)

Whatever the cause, the ferocity and resilience of the Vampires made their defeat very difficult, even for the Time Lords. Conventional weapons were virtually useless, and at this point the Time Lords did not have access to some of the more spectacular armaments they later developed.

The weapon which won the war was the bowship. Rassilon ordered the construction of these ships to exploit the one weakness of the Great Vampires — their vulnerability to being impaled through the heart. Nevertheless, hunting down the entire species was a protracted business. Eventually, all but one — the leader — were found and destroyed. (DW: State of Decay)

According to the Remote transmission, near the end of the war Omega created shells around the black holes which the Vampires had used to enter the universe, blocking them off and making the former black holes resemble ordinary planets — unless someone attempted to drill to the planet's core. (EDA: Interference - Book One)

The war caused such widespread loss of life that the Time Lords rejected the use of violence forever. (DW: State of Decay)

After the Vampires' defeat, their legend and elements of their story existed in many cultures, including Earth, where Vampire legends also existed among the populace. (MA: Goth Opera, EDA: Vampire Science)

The Fourth Doctor effectively ended the war by killing the King Vampire, who had fled into E-Space. (DW: State of Decay)