Lucius is a legendary 2nd-century King of the Britons and saint traditionally credited with introducing Christianity into Britain. Lucius is first mentioned in a 6th-century version of the Liber Pontificalis, which says that he sent a letter to Pope Eleutherius asking to be made a Christian. The story became widespread after it was repeated in the 8th century by Bede, who added the detail that after Eleutherius granted Lucius' request, the Britons followed their king in conversion and maintained the Christian faith until the Diocletianic Persecution of 303. Later writers expanded the legend, giving accounts of missionary activity under Lucius and attributing to him the foundation of certain churches. There is no contemporary evidence for a king of this name, and modern scholars believe that his appearance in the Liber Pontificalis is the result of a scribal error. However, for centuries the story of this "first Christian king" was widely believed, especially in Britain, where it was considered an accurate account of Christianity among the early Britons. During the English Reformation, the Lucius story was used in polemics by both Catholics and Protestants; Catholics considered it evidence of papal supremacy from a very early date, while Protestants used it to bolster claims of the primacy of a British national church founded by the crown.
The now orthodox view of Lucius has been challenged by Southampton University educated archaeologist David J. Knight in his book 'King Lucius of Britain', where Knight suggests that Abgar was King of Edessa, not ‘Britio’, which was the local name for a castle within his realm, Knight suggests that he is never called Lucius of Britio/Birtha in contemporary sources, only Abgar of Edessa. Knight argues for accepting the ancient tradition, that the Lucius who wrote to Pope Eleutherius was a British ruler.
The legendary first bishop of Chur and patron saint of the Grisons was also named Lucius, with whom the British Lucius is not to be confused. It is possible, however, that the mentioning of Saint Lucius of Britain in the Liber Pontificalis soon led to a scholarly identification of the otherwise somewhat shapeless patron saint with his more prominent British namesake. His supposed relics are still kept in the cathedral of Chur, although there is little doubt among scholars that the bishopric was only established some 150 years after its alleged founder was martyred.