Immortal Army

Across history, there has been two immortal armies created with the magic of the Cup of Life.

Warlord's army
Many centuries ago, the Cup of Life fell into the possession of a great warlord. One night, he gathered his army before him. He took a drop of blood from each and every man and collected it in the Cup. Such was the vessel's power that the soldiers were made immortal where they stood. According to Gaius, the carnage they wrought was beyond all imagining. The army was only defeated when the Cup was emptied of the blood it contained (The Coming of Arthur: Part One).

Cenred's army
Morgause, High Priestess of the Old Religion, formed an alliance with the King of Escetia, Cenred, who she used to get her hands on the Cup of Life. Once she succeeded, she collected a drop of blood from each man of Cenred 's army in the Cup, making them immortal. Morgause then turned one of Cenred's men against him, eventually killing the King. The army marched on Camelot, and due to their new gift, crowned Morgana Pendragon Queen of Camelot (The Coming of Arthur: Part One).

When Guinevere and Leon escaped from Camelot and headed for the cave in which Arthur and his companions were hiding, Morgause and a group of immortal soldiers followed them, thanks to the potion Morgana had secretly given to her maid, which allowed her to magically track Gwen. Although Arthur, Merlin, Gaius, Gwaine and Elyan were attacked by the immortals, they were able to flee, with Lancelot and Percival's help. In this occasion the young warlock had the chance to use the sword Excalibur and see that the magical blade had the power to kill the undead. Cenred's men were, in fact, the living dead, for they had toyed with the Cup of Life.

When Arthur and his new knights entered the castle of Camelot to save the imprisoned King, the alarm was inadvertently sounded and the Prince and his allies found themselves trapped; surrounded by the immortals, they decided to go down fighting. Meanwhile, Merlin and Lancelot fought their way to the throne room, the sword easily destroying any immortals. However, as Merlin reached the Cup and was about to spill the blood, Morgause appeared and used her magic to stop him. Luckily, thanks to Gaius' intervention, Merlin was able to smash the High Priestess into a pillar, seriously injuring her. Merlin then used the sword to knock the Cup of Life over, spilling the blood within and breaking the enchantment; all over Camelot, the immortals instantly perished as the spell was broken (The Coming of Arthur: Part Two).