The movie presents a reimagining of the legend of King Arthur, portraying him as a Roman cavalry officer leading a band of knights known as the Sarmatian knights in Britain during the declining days of the Roman Empire.
Arthur (played by Clive Owen) and his knights, including Lancelot (played by Ioan Gruffudd), Gawain (played by Joel Edgerton), Galahad (played by Hugh Dancy), Tristan (played by Mads Mikkelsen), and Bors (played by Ray Winstone), are stationed along Hadrian’s Wall in Northern Britain, where they defend against incursions by the Woads, a group of native Britons led by the mysterious Guinevere (played by Keira Knightley).
In the climax of the film, Arthur and his knights are ordered by their Roman commander, Bishop Germanius (played by Ivano Marescotti), to embark on one final mission before being relieved of their duties. They are tasked with rescuing a Roman family trapped behind enemy lines and escorting them to safety in Roman territory.
However, Arthur and his knights soon discover that the mission is a trap set by Bishop Germanius, who plans to use them as bait to draw out and eliminate the Woads. Feeling betrayed by their Roman masters, Arthur and his knights choose to fight alongside the Woads in defense of Britain and its people.
In the ensuing battle, Arthur and his knights emerge victorious, but at a great cost. Lancelot sacrifices himself to save Guinevere, while Tristan dies in battle defending the group. Despite their losses, Arthur and his remaining knights, along with Guinevere and the Woads, rally together to defend Britain against further Roman incursions.
In the end, Arthur chooses to renounce his allegiance to Rome and pledges himself to the defense of Britain and its people, fulfilling his destiny as the legendary King Arthur.
Overall, “King Arthur” is a gritty and action-packed retelling of the Arthurian legend, focusing on themes of loyalty, honor, and the struggle for freedom. With its epic battles, complex characters, and stunning visuals, it offers an exciting and immersive movie experience for audiences.