Many centuries ago, a great warlord collected a drop of blood from each of his soldiers and due to the power of the Cup the army was made immortal, causing unimaginable carnage. Only when the Cup was emptied of the blood that it contained was the enchantment broken and the army destroyed (The Coming of Arthur).
The Balance of Life and DeathEditIt is possible that the Cup was kept by the High Priestesses of the Old Religion on the Isle of the Blessed. When Arthur was bitten by a Questing Beast, Merlin travelled to the Isle of the Blessed in order to sacrifice his life to save Arthur's. Nimueh called upon the gods to bring rain with the spell "Tídrénas!", which filled the chalice, and the water was taken to Arthur so that his life would be spared. When Gaius came to the Isle of the Blessed to offer his life in order to save Merlin, Nimueh used again the Cup to summon the power over life and death with the invocation "Ic, séo héahsácerd, þe ácwele strengþe ealdan æwfæstnesse!" Merlin then came to the Isle of the Blessed and killed Nimueh, saving Gaius (Le Morte d'Arthur). Merlin thought that the Cup was destroyed when he killed Nimueh. The Cup, however, remained and fell into the possession of a group of Druids located past the border into Cenred's kingdom.
Morgause revealed to Morgana that she had searched for it for a long time. It is unknown whether her search took place while the Cup was in Nimueh's hands (The Coming of Arthur).
In the Hands of EvilEditA patrol of Camelot knights led by Sir Leon was slaughtered by Cenred's soldiers for trespassing onto their land. The druids arrived afterwards and gave a wounded Sir Leon water from the Cup of Life which saved him from death. They chanted in chorus this spell: "Butan þæt cwalu. Hrðe þon aidlian. Hrðe þon eðian. Bot ond tile". When Sir Leon informed King Uther and Arthur of this, Uther decided that the Cup must be recovered before Cenred found it. Arthur and Merlin joined forces with Gwaine and found the Druids, who gave them the cup. Cenred, however, with information from the slave trader Jarl, who previously captured the trio, sent a group of knights to capture the cup. They succeeded and Morgause used it to turn Cenred's army into immortals. She had each and every soldier put a drop of his blood in the Cup, after she had chanted these words: "Gegadre anne here fram þisse bune ond heora blod. Swa þæt hie ne abygð ond ne swilteaþ naht, ac leofaaþ a on ecnesse". She usurped control of the soldiers from Cenred in the process, and had one of them kill him with the spell "Ic bebiede þe ðine cyning cwellan!" She then used the army to conquer Camelot and put Morgana on the throne (The Coming of Arthur).
Merlin asked Gaius if he knew more about the legend of the Cup of Life and how to eliminate Morgause and Morgana's immortal army. Gaius informed Merlin that if the cup was to be overturned and the blood it held spilt, the army would no longer be immortal. Upon hearing this, Merlin conspired with Lancelot to focus their efforts on obtaining possession of the Cup of Life. When they arrived at the throne room, it was protected by numerous soldiers. Using Excalibur, Merlin destroyed the guards and almost succeeded in tipping the Cup, but Morgause arrived and magically threw him aside. However, the timely arrival of Gaius prevented Morgause from destroying Merlin. Merlin managed to use his magic to slam Morgause into a pillar, rendering her unconscious. He then used Excalibur to knock the Cup of Life off its pedestal, spilling the blood it contained. The Cup of Life's current location is unknown (The Coming of Arthur).
In the LegendsEdit
The Cup of Life is likely an allusion to the legends of the Holy Grail, commonly affiliated with King Arthur and his knights. Although Christianity is never directly referenced in the series, frequent mention is made to the Great Purge, wherein Uther appears to have removed not only magic from the land but also the Old Religion itself.