King Arthur: Knights and Vassals DLC

"The legend of the Once and Future King is as ancient as the realm of Britannia itself. It tells about the arrival of a great king who will unite the warring kingdoms of the land and bring peace and prosperity to all."
New units become available after the completion of the "Lady of the Lake" objective:

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Briton Archers — Facing constant warfare, the Britons realized that they need some archers who are trained in the art of melee.

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Briton Cavalry — These devoted horsemen ride out into the hidden corners of Britannia to bring back rumors. In battles their heavy armor gives them excellent protection, but also slows them down a bit.
New units become available are available after the conquest of either Norfolk or Norgales:

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Saxon Knight: unlocked after conquering Norfolk — When the Saxons decided to follow the other courts of Britannia and established the knighthood in Norfolk, they only allowed the best warriors to join these ranks.

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Welsh Pikemen: unlocked after conquering Norgales — Equipped with a shield and a pike, these tribal warriors from the kingdom of druids are not only good fighters but they are quite resistant to the power of magic.
Two powerful Knights join the Round Table when the first Stronghold is built:

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Sir Alymere — This knight was destined to be a great champion and indeed, he became one of the most respected wandering knights.

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Sir Lucan — Lucan was a regular participant of the royal tournaments and bravely defended the lands of his family during the chaotic times after the Miracle.