High Priestess

“[...] For ordinary gifts were not enough. Only those possessed of exceptional magical power could ever hope to be one of The Nine.”

— Gaius about the High Priestesses^[src]

The High Priestesses of the Triple Goddess were one of the most important figures of the Old Religion, 

A High Priestess of the Old Religion.

a group of nine sorceresses who held control over the other wielders of magic, and were worshiped by them.

The High Priestesses were extremely powerful magical beings: Morgana herself declared that, as High Priestess, she had the power of the heavens in her hands (Arthur's Bane: Part Two). She also claimed that no mortal weapon could kill her, justifying her survival of the many wounds that had been inflicted on her on different occasions (The Diamond of the Day: Part Two).

History

The High Priestesses were the chief servants of the Triple Goddess. They were a group of highly skilled and powerful sorceresses, mistresses of magic and spells and detained the power over life and death. They lived on the Isle of the Blessed, where they guarded the Cup of Life (at least, it is clear that the Cup was in Nimueh’s possession during Series 1. It is unknown, though, how the Druids got their hands on it after her death). They were served by the Blood Guard and they guarded the Rowan Staff, a powerful magical instrument carved from the Rowan Tree that grows at the very heart of the Isle of the Blessed. The Rowan Tree was of much significance to them and is the symbol of the Blood Guard.

On Samhain Eve, at the time of the Old Religion, the High Priestesses performed a blood sacrifice to open the Veil between this world and the Spirit world and release the Dorocha (The Darkest Hour). They also used dark magic to summon from the depths of the Underworld the Fomorroh, a creature that they revered. This would allow them to take over the minds of their enemies, binding them to their will (A Servant of Two Masters).

It is possible that the Crystal of Neahtid was kept and guarded by the High Priestesses on the Isle of the Blessed, before it was taken by Uther and locked into the vaults of Camelot. The many sorcerers who died trying to protect it could have been the High Priestesses and their followers (The Witch's Quickening).

According to Gaius, a long time ago, a war broke out between the High Priestesses and the ancient Kings. The sorceresses took the blood from a girl and mingled it with that of a serpent. The creatures they created had ferocious powers. They could control the mind of a man, suck the life from him and transform at will into hideous monsters. Eventually, the High Priestesses themselves lost control over the Lamia, which lead to the deaths of many lives (Lamia).

Although being extremely gifted seers, according to Kilgharrah the vates' power of prophecy was unrivaled, even by a High Priestess (Arthur's Bane: Part One).

The Horn of Cathbhadh was kept by the High Priestesses on the Isle of the Blessed, but when Uther attacked them, the Horn was smuggled to safety before the temple fell. According to Gaius, who had taken part in such ceremonies, long before the time of the Great Purge, each year at Beltane the High Priestesses would gather at the Great Stones of Nemeton and summon the spirits of their ancestors. In the days of the Old Religion, however, the priestesses trained for years before entering the Spirit World, since it was fraught with dangers. The one thing they were schooled never to do was to look back at the spirit, as the Veil closed. If they had done it, they would have released the spirit into this world (The Death Song of Uther Pendragon).

Certain mysteries of the Old Religion were revealed only to a handful of female initiates, destined to become High Priestesses. Among these was the ancient ritual of the "Teine Diaga", the "sacred fire", which used the mandrake root to bring unimaginable terror to the victim (their screams could be heard twenty leagues away). When it was finally over, their will was no longer their own, they were slaves of the High Priestesses for eternity (With All My Heart).

In the old days the sorceresses also used to perform a terrible punishment known as Ragaid, the ultimate warning from the High Priestess to her enemies. The disfigurement was the result of extremely powerful magic and caused the skin to grow across the victim's face until he suffocated. Morgana performed this magic on a Knight of Camelot to declare war to the whole kingdom (The Kindness of Strangers).

When Uther and Camelot turned against magic and the Old Religion with the Great Purge, most of the High Priestesses were wiped out and slaughtered. The ones that survived hid themselves away, and from that moment they used their powers to try to bring about Camelot’s downfall.

Known Priestesses

Morgana and Morgause, two High Priestesses.

Until the episode The Secret Sharer, it was unknown how many of the nine High Priestesses were left after the Great Purge. Alator of the Catha, warrior and High Priest, revealed that Morgana was the last remaining High Priestess of the Triple Goddess. The other known High Priestesses before Morgana were:

• Nimueh †
• Morgause †

Morgana

It remained unclear whether or not Morgana was a High Priestess during Series 3, though it seemed unlikely as her

Morgana Pendragon, last High Priestess of the Triple Goddess.

control over her powers was in its infancy. However, being Morgause’s sister, the sorceress’ Blood Guards (at the entrance of Morgause's cave) treated her with reverence.

It became clear that during her time away from Camelot with a weakening Morgause, Morgana had become a High Priestess, having mastered many different aspects of magic and proving to able to perform the blood sacrifice of Samhain (The Darkest Hour). Morgana gained full control of her magic and gained extensive knowledge of the Old Religion.

In the three years between Series 4 and Series 5, Morgana's powers had grown significantly as she was able to knock out Merlin with one stunning spell in his young form (whereas in Series 4 she couldn't with two stunning spells in his aged form (Arthur's Bane, A Servant of Two Masters). She had become even more confident in her magic, showing an incredible power when she held an ageing spell for at least four days, which even Merlin found exhausting, and her knowledge about the Old Ways had also grown too. 

She was probably the only High Priestess ever to, although not being a Dragonlord, control a dragon: Aithusa had chosen to be at Morgana's side and was deeply attached to her mistress and companion.

Morgana was killed by Merlin with the sword forged in the Great Dragon's breath, Excalibur. Her death marked the final extinction of the High Priestesses (The Diamond of the Day: Part Two).

Morgause, brought up by the High Priestesses.

Morgause

Morgause, Vivienne’s daughter, was smuggled out of Camelot at birth and given to the High Priestesses by Gaius, who was probably their friend and maybe their servant, when Uther ordered her execution. The remaining High Priestesses taught her magic and how to master her powers. They probably instilled in her the hatred for Uther, Camelot and Arthur, and told her about her half-sister Morgana and her parentage. In the beginning of the episode The Sins of the Father, Morgause was found living in a ruined castle. It is possible that there is where she was brought and where the High Priestesses dwelt. Morgause was an extremely powerful sorceress, skilled in many different aspects of magic, with a particular brutal force. She was able to wield the Cup of Life and mirror life and death.

After her magical duel with Merlin and Gaius, she was badly wounded and condemned to a slow and painful death (The Coming of Arthur: Part Two). Not wanting to live like a cripple for the rest of her short life, she decided to let Morgana sacrifice her on the Isle of the Blessed, so that the Witch could tear the Veil between the worlds. She had spent a year teaching Morgana magic, and after her death her sister became High Priestess (The Darkest Hour).

Nimueh

Nimueh, former ally of Camelot.

Nimueh was a hydromancer and probably the last remaining High Priestess before Morgause. She had been a friend of Uther and Camelot before the Great Purge and the court sorceress. Her bargain with the King and the following death of the Queen started Uther’s war against magic. She tried many times to destroy the kingdom, but she was killed by Merlin with a lighting bolt on the Isle of the Blessed. Nimueh was an extremely gifted and powerful Priestess. She dwelt on the

Nimueh, the first High Priestess to appear.

Isle of the Blessed and guarded the Cup of Life. With this magical vessel, she could summon the gods of the Old Religion and alter the balance of the world, harnessing the power over life and death to her own (Le Morte d'Arthur). She was also the only High Priestess to discover Emrys’ identity.

The Bendrui

The Bendrui was a group of priestesses who trained 

The symbol for the Bendrui, which was also tattooed on Finna's wrist.

to become High Priestesses but failed to meet the exceptionally high standards.

According to Gaius, before the time of the Great Purge girls would be chosen at birth for the priesthood. They'd be taken away from their families and brought up as initiates in the Old Religion. When Merlin asked Gaius if Finna was a High Priestess, the physician answered that, although many tried, few succeeded, for ordinary gifts were not enough: only those possessed of exceptional magical power could ever hope to be one of the Nine.

Finna.

Finna was probably the last priestess of the Bendrui to be alive at Merlin's time. She was practiced in potent magic and Gaius believed she could feign any look she wished. Finna regarded both Merlin and Alator as her masters, even onto worshiping the figure of Emrys. Although she had spent a lifetime running from Uther and Arthur, she wanted to help Merlin bring about Albion's golden age. She had been given by Alator a sacred piece of parchment containing a prophecy about the battle of Camlann and had been instructed to give it to Emrys, along with the warning not to trust the druid boy Mordred. She killed herself with Merlin's sword so that Morgana wouldn't be able to torture her into revealing Emrys' identity (The Kindness of Strangers).

Powers and Abilities

High Priestesses are exceptionally skilled at Magic. According to Morgana, a High Priestess could not be killed by a mortal weapon, only magic. This statement is supported by the fact that both of the other High Priestesses were killed using magic, and while she received many should-be mortal wounds from mortal blades, she did not die until stabbed with Excalibur, an enchanted weapon able to kill anything, mortal or magical.

Trivia

• It is possible that Vivienne, Morgana, and Morgause’s mother, had been a High Priestess. In the episode The Secret Sharer, Morgana told Alator that her healing bracelet had been forged on the Isle of the Blessed by a High Priestess. This bracelet had been given to Morgana by her sister, who had told her it belonged to their mother. Considering this, the owner and the maker of the bracelet may have been the same person (Vivienne).
• All three High Priestesses wore red at one time or another.
• All three High Priestesses have used scrying, but all in different forms: Nimueh performed hyrdomancy, Morgause used crystallomancy and Morgana oneiromancy.