Blood Druids
In the past the Angharad practiced their religion differently. Their connection to the gods was more tenuous and they did not know the correct prayers and rituals to forge connections to them.
During those times the Angharad used more sacrifice to make that connection to the divine, including human sacrifice. This made connections more difficult, but when made were very strong. For a time blood was a common component of much of their magic.
Eventually, new prayers were found and the negative impacts of the blood rituals on society and even to nature took its toll and there was conflict in the Circle. One faction held onto the primal blood rituals and another embraced the new methods.
After a lengthy struggle between the factions that involved the summoning of an Avatar of Arawn (The Wild Hunt), the old "Blood Druid" faction lost in a climatic battle at the Temple of Silvanus. The Temple of Silvanus became cursed after this conflict and is one of the "Lost Temples" of the Angharad (the other being the Temple of Selene). The time of this transition is sometimes called the Great Reformation.
Now most of the history of this time in Angharad history has been forgotten by the common man, but is generally known by members of The Circle and those who study history. There are still some old cultish remnants of the Blood Druids that crop of periodically...
Also see Angharad Religion.