The Lhiannan were a territorial, matriarchal and druidic Cainite bloodline who existed in the Dark Ages. Though they are believed to have been an offshoot of Clan Gangrel, they themselves did not believe they were descended from Caine at all, but instead believed they were made by the "Crone", a mysterious figure who may be the same Crone mentioned in the Book of Nod.
The true origins of the Lhiannan are shrouded in mystery, though Kindred outside the bloodline generally agree they must be descended from the Gangrel. According to their own lore, the first Lhiannan was created when the Crone infused a woodland spirit into a vampire. This spirit was said to be a desperate, jealous being that could apparently see that people would destroy the forests and burn the trees that comprised them. Joining with an undying predator, then, was apparently the spirit's attempt at dodging this fate. Whether or not any of that is true, the Lhiannan did have a connection to the natural world that no other vampire, not even the Gangrel, could equal.
Most other vampires viewed the Lhiannan bloodline as little more than savages, and rarely bothered with them. The Gangrel however, viewed them with intense hatred and slew them whenever possible. The Gangrel were characteristically tight-lipped about the reasons for their vitriol, but would sometimes speak of a "great betrayal" when referring to the Druids. Magda, possibly the eldest remaining Lhiannan in existence at that point in time, resided in Ireland and repelled attempts on her unlife.
In the Dark Ages the Lhiannan dwindled increasingly in number. The Lhiannan found it harder to prey on humans, who congregated in cities away from the old places of the woods.
The bloodline was never numerous (especially since creating a new Lhiannan meant that the sire grew weaker), and as the power of the Christian church stamped out the old ways, the Druids were unable to flee the wrath of the Inquisition, who found them easily thanks to their otherworldly auras and obviously pagan rituals. By the time of the War of Princes it was thought that perhaps only twenty Lhiannan remained in all of Europe, and none were believed to have survived past the end of the 14th century.
In modern times, Gangrel trade rumors of powerful Kindred in European forests decorated with strange, bloody symbols, so perhaps some of them survived, or perhaps the forest spirit that initially created the bloodline has resurfaced.
The Lhiannan were part nature spirit, and so had a unique connection to the world of spirits, most notably in the form of their Discipline Ogham; this connection gave them an inhuman aura obvious even to humans (and it was exceedingly easy for others to gauge their natures through the use of Auspex).
They were also bound to the land, unable to leave their chosen woodland territories for long without becoming weak, with their powers and physical abilities reducing in strength for roughly every week they were gone from their home. Once they returned, they quickly regained their previous strength in only a few hours.
Finally, all Lihannan weakened themselves by siring; whenever a Lhiannan embraced a childe, the spirit inside the sire would break off a piece of itself and make it into a new spirit and passed it into the new vampire, and thus both sire and childe would end up with the power of a split spirit. And with each Lhiannan destroyed, a piece of the spirit disappears forever.
The Lhiannan were highly solitary, irrevocably bound to their wild territories. Occasionally a small brood of newer, younger Lhiannan would share a territory as they would be weaker than their forebears and thus might feel the need to pool their resources and strength in order to protect a given area.
The Lhiannan were generally aware of members of their bloodline whose territories were adjacent, but there was no system of communication in place. This, of course, may have contributed to their eventual destruction. That said, most Lhiannan had a wary truce with one another, and would often allow other members of the bloodline to quickly travel through their territories if the need arose.
All Lhiannan followed a variation of pagan and druid practices, and were closely tied to their personal territory, growing weak if they left it for longer than a few days, and sometimes even becoming violently ill if they entered human cities. They made chiminage to the local spirits to keep themselves strong, mostly in the form of blood sacrifices.
The bloodline had few enemies outside of human civilization and the rising of Christianity, though the Gangrel were noted for often attacking Lhiannan on sight, whereas most other Cainites left them alone, favoring the nights in the cities as opposed to the ever-diminishing forests.
Lhiannan were matriarchal, and nearly all of their number were females; this was because of their belief in being descended from the Crone, as females tended to be perceived as being closer to the "Dark Mother".
With their numbers so small, and as they are weakened by the act of the siring a childe, Lhiannan rarely gave the Embrace; the Druids only created childer out of sheer loneliness or when they found someone who truly impressed them. A pagan spirit-speaker with real devotion to her craft, or a woodsman with impeccable respect for the forests might be enough to get a Lhiannan's attention. The Lhiannan refused to Embrace Christians, Jews, or Muslims.
Once a Lhiannan Embraced a childe, she generally kept the new vampire around for a few years until that childe was ready to fend for himself (and the novelty of having someone else around wore off). The sire would then send the childe away to find his own haven and territory.
The Lhiannan made their havens in the forests of Europe, constructing simple dwellings or finding natural shelter. They would sometimes find a man-made haven and kill or enslave the inhabitants, or very rarely eke out an existence on the periphery of human civilization by taking the role of a shaman or wise woman.