Arthur, merlin and the other rebels.
This event was when Arthur created a rebellion to save Camelot from Morgana, who had taken over Camelot.
Prelude
When Arthur and Merlin failed in their mission to find the Cup of Life and when it fell into the hands of Morgause, she made Cenred's army immortal. After using the immortal army to capture Camelot, Morgana was crowned Queen after Morgause removed Uther Pendragon's crown. Arthur and Merlin along with Gaius, Gwaine and Elyan hid in the outskirts of Camelot. Gaius told Merlin that the only way to overthrow Morgana would be to destroy the immortal army by emptying the Cup of Life of the blood within. After seeing Freya again by using water from the Lake of Avalon, Merlin went to get the sword Excalibur from the Lake of Avalon with Kilgharrah's help. The sword was the only weapon which could destroy the immortal army. Meanwhile Gwen escaped Camelot with Sir Leon and narrowly escaped the immortal army with help from Lancelot and his friend Percival. Arthur later knighted Gwaine, Percival, Lancelot and Elyan. Lancelot then chose to join Merlin in his mission to find the Cup of Life.
The Rebellion
Arthur was joined by Merlin, Lancelot, Gwaine, Elyan, Percival and Sir Leon in his attempt to save Camelot. Gaius then mysteriously dissappeared, much to Gwens worry. Merlin and Lancelot then split up to find the Cup. Arthur along with the knights succeeded in finding Uther but they got caught by the immortal army. meanwhile Merlin and Lancelot succeeded in finding the Cup of Life after Merlin killed some immortals with Excalibur. However Morgause arrived and attacked Merlin with her magic while Arthur and his knights were struggling to fight against the immortal army. At this moment Gaius, who had been following them, attacks Morgause with his magic, allowing Merlin to defeat or possibly kill her. Merlin then emptied the Cup of Life, finally destroying the immortal army and saving Arthur and the other knights. Morgana then arrived and brought the room crashing down with her magic while holding Morgause, forcing Merlin, Gaius and Lancelot to escape. (The Coming of Arthur).
Aftermath
After the battle, peace was restored to Camelot. Gwen later returned to Camelot and kissed Arthur in front of the knights. Gaius later told Merlin that there was no sign of Morgana or Morgause, indicating that Morgana managed to escape with Morgause's body. After that Merlin put Excalibur into a stone where no ordinary man could weild it.