Sword of Peace
In the Alliterative Morte Arthure, a magnificent sword kept by Arthur in a vault at Wallingford. This was a sword only to be used for ceremonies, such as knightings.
Unlike Excalibur, Clarent represents the authority of the king in times of peace rather than war. It is associated with King Arthur’s role as a just ruler and is often mentioned in accounts of the Round Table.
Other than Arthur, only Guenevere knew of its location; therefore, when Arthur saw Mordred wielding it in battle, he knew that Guenevere had betrayed him. Mordred carried it throughout the war with Arthur, and perhaps killed Arthur with it.
Source
Alliterative Morte Arthure | c. 1400