In the Hunter's HeartEditThe Southrons first appeared in the eleventh episode of Series 4, where they stormed a village in search of new recruits. Most of the people in the village were not willing and, so, were presumably killed. A soldier was about to kill Gwen before Helios stopped him, deciding to keep Gwen as a prisoner. What the soldier was about to do before Helios intervened shows just how hard-hearted the soldiers were. This was likely due to an upbringing or training where they were taught to stop at nothing and show no mercy or exception when undergoing missions, similar to the ways in which men were raised in ancient Sparta.
When Gwen escaped from the Southrons' hideout, Helios and Morgana rode into the forest and Helios ordered his men to scour the forest, which they did without delay. After no success, Morgana then told Helios to order them back. Helios whistled and they all returned.
In The Sword in The Stone: Part OneEdit
The Southrons prepared to undergo their takeover of Camelot. Agravaine used fire signals to lead them to the gate without being suspected. They broke in through the secret tunnel, killing a few guards and knights on the way without being detected by them. They then spilled oil everywhere and set it on fire. It is unknown how many people the Southrons killed during the takeover, but in The Sword in the Stone: Part Two it is revealed that many ran into the forest. Arthur, Gwaine, Elyan, and the rest of the knights overpowered a large number of Southrons, but Arthur's arm was injured in the process. It took the Southrons a while to get to where Arthur, Gaius, Merlin, Percival, and Gwaine were hiding and when they eventually broke into the room, all they found were Gwaine and Gaius, who were captured without being killed, since Morgana, who was present, decided to imprison them. After failing to catch Arthur in Camelot, Morgana immediately ordered a for Arthur to be hunted, as if she was planning a hunt for an animal. The Southrons hastened to the valley of the fallen kings and, out of the refugees, only Arthur and Merlin escaped. Elyan, who they met on the way, chose to stop to hold the Southrons off to ensure Arthur wasn't caught. He ended up giving himself up.
Elyan was taken back to Camelot, to Morgana's throne room, and tortured with a Naithar. He reluctantly revealed Arthur's destination, the village of Ealdor, and Morgana ordered Agravaine to go there with a large squad of Southrons, threatening that, if he were to fail, he would take Elyan's place as a tortured prisoner. Agravaine appeared displeased with his position, feeling the weight of a large deal of responsibility on his shoulders. He later visited Morgana before he left, giving her his last words. She questioned if they were prepared and he said the Southrons were already ready to take off but were waiting for him to lead them.
The Southrons arrived at Ealdor not long after, the majority surrounding the place as Agravaine and a bunch of soldiers entered, pushing people out of the way, wanting only Arthur and his group. Merlin used magic to distract Agravaine and the Southrons as they ran out of the village. The Southrons then left Ealdor completely, leaving little damage.
The Sword in The Stone: Part TwoEditThe Southrons chased Arthur, Merlin, Gwen, Isolde, and Tristan into a cave near Ealdor. Merlin, on the way, ordered Kilgharrah to attack the Southrons. Only a few survived, including Agravaine. The surviving Southrons, lead by Agravaine, pursued the refugees into the caves, but the Southrons had no sense of direction in the dark labyrinth. Merlin went back to create a diversion, calling for their attention, then luring them towards him. After Agravaine, who had discovered Merlin's magical secret, threatened Merlin with death, Merlin killed him and the remaining Southrons with a couple of magical blasts.
Back in Camelot, the Southrons were using Gwaine as their entertainment, making him fight in unfair circumstances, such as against several strong, heavily armed men while only equipped with a short wooden sword. Gwaine won each fight. The men were willing to give up their lives just for Morgana and the rest of the Southron's entertainment, showing they either didn't value their life, or they were blindly desperate to please their masters, or overly confident that they could beat Gwaine, who was without armour, either feebly armed or unarmed, starved, and exhausted from multiple fights.
When Merlin, disguised as Dragoon, snuck back into Camelot to place a poppet under Morgana's bed, only one Southron, a hooded one, managed to get close to him. Merlin killed him and used his uniform as a disguise to escape Camelot.
The knights later invaded Camelot to take it back and were mostly successful. Helios was defeated by Isolde, who stabbed him in the back just as he was about to slay Arthur, but he rebounded, killing Isolde. When Morgana was defeated by Merlin after losing her magic, it is unknown how many Southrons remained. Many may have fled due to their masters having been being defeated.