LUCIUS, a legendary hero, is called the first Christian king in Britain, and is supposed to have lived in the second century. There is no record of his existence until three or four centuries after his supposed death; the story that Pope Eleutherus received a letter from Lucius, a British king, announcing his conversion to Christianity, originated in the fifth or sixth century, and appears in the ‘Catalogus Pontificum Romanorum,’ written about 530 (Acta SS., 1 April, i. xxiii). The original ‘Catalogus,’ written shortly after 353, says nothing about it. Beda copies the story (Hist. Eccl. i. 4, v. 24), and in Nennius's ninth-century account, the earliest British testimony, Lucius is identified with Lleuer Mawr, a chieftain in South Wales, whose name, expressing the idea of brightness, corresponds to the Latin Lucius. In the Welsh triads and genealogies, whose date is uncertain, this chieftain is called the founder of the church of Llandaff (Myv. Arch. ii. 63, 68), and the names of Dyfan, Ffagan, Medwy, and Elfan, possibly real personages, are given as those of the messengers Eleutherus sent from Rome (Achau y Saint); the ‘Book of Llandaff’ (ed. Rees, pp. 65, 310) calls the first two Lucius's messengers to Rome. The Welsh stories want detail, and there is nothing improbable in their account if earlier authority for Lucius's existence were forthcoming.
The legend of Lucius owes its wealth of detail to Geoffrey of Monmouth; the greater part of his narrative is at direct variance with authentic history, and the whole must be rejected. William of Malmesbury in all probability had no sure authority for connecting Lucius with Glastonbury. By the fourteenth century a letter to Lucius from Eleutherus had been forged (Spelman, Concilia, i. 31), and by the seventeenth century a gold coin, now in the British Museum, and a silver coin, purporting to have been issued from Lucius's mint, had also been manufactured (Ussher, Brit. Eccl. Ant. v. cc. iii. sq.) After the twelfth century Lucius appears frequently as a benefactor to the church, and later still to the university of Cambridge. Confusion with a continental teacher of the same name explains the stories of his missionary labours abroad and of his martyrdom (ib.)
[Haddan and Stubbs' Councils, i. 25, 26; Dictionary of Christian Biography, s. v.]