Knights of the Round

The Knights of the Round (ナイトオブラウンズ, Nait ō bu Raunzu) or formerly known as the 12 Horsemen is a unit of twelve elite soldiers in the Holy Empire of Britannia, each being assigned into the group by royalty and under direct command of the Emperor. The Knights of the Round extends to at least the 18th century, with the first Knight of One being Sir Richard Hector. Named after the Arthurian Knights of the Round Table, they operate outside the standard Britannian military and are given special privileges and authority.

Privileges
Aside from the Knight of One, there were no known distinctions in privileges between the numbers as they existed in the era. The Knight of One may request governance of any colonial area of his choosing from the Emperor. After a person is captured for assaulting a knight, the knight can then decide the fate of the captured person, as seen after an attempt to assassinate Suzaku by an Eleven; he was asked for the severity of the punishment for the Eleven. Only eight of the twelve Knights have been revealed. The Code Geass novels explain that not all of the seats are filled, so those featured might be the only active members. A Knight of the Round cannot be punished for his crimes by anyone other than the Britannian Emperor, as shown when Schneizel was unable to punish Suzaku for meeting with Lelouch behind his back.

A special title, the Knight of Zero, was created by Lelouch vi Britannia following his ascension to the throne. This title was specifically given to Suzaku Kururugi, who was thereby classified as a Knight of the Round above all others, giving him the highest authority as a Britannian Knight, even over the Knight of One.

Code Geass: The Manga
Knights of the Round have lesser emphasis in the manga due to the appearance of Suzaku, Gino, and Anya. They appear to have dissolved due to Emperor Lelouch's ascension to the throne as well as after Zero Requiem

Nightmare of Nunnally
In the manga spinoff Nightmare of Nunnally, a group of former knights of the kingdom are revived by Charles zi Britannia's Geass "The Dead Rise." They each pilot Sutherland Sieg-like Knightmares. The only named member of this group is Bismarck Waldstein.

Lost Colors
In the spinoff game, Code Geass: Lost Colors, Nonette Enneagram appears as a Knight of Round and acts as a mentor to the protagonist character. Her appearance in Code Geass R2 is a salute to her appearance in the game, despite not having any role in the anime.