Lucius Artorius Castus (fl. 2nd century) was a military commander of ancient Rome, suggested by some as the historical basis for King Arthur.

What is known of Artorius comes from inscriptions on fragments of a sarcophagus, and a memorial plaque, both found in Podstrana on the Dalmatian coast. Although undated, the likely time period of the sarcophagus (before 200), combined with the inscription's mention of Artorius being a dux, suggests that he was the unnamed commander of a 185 expedition to Armorica mentioned by Herodian.

As a member of the gens Artoria he was likely a native of Campania, a region of Southern Italy. According to the inscription, Artorius was a centurion of the Legio III Gallica, then moved to VI Ferrata, then to V Macedonica, where he was promoted to primus pilus. He was then made praepositus of the classis Misenensis (the Bay of Naples fleet), followed by a position as praefectus of the VI Victrix.

The VI Victrix was based in Britain from c. 122. Artorius likely participated in the guarding of Hadrian's Wall. It has been suggested that this was possibly from Bremetennacum with a contingent of Sarmatians, but there is no clear evidence for this. When VI Victrix mutinied, Artorius seems to have remained loyal, since Pertinax soon after promoted him to dux and sent him to Armorica with several cohorts of cavalry, where he was successful in suppressing an uprising.

Artorius then retired from the army and became procurator centenaris (governor) of Liburnia, a part of Dalmatia. Nothing further is known certainly of him, although the father of Cassius Dio was governor of Dalmatia while Artorius was in Liburnia, and some of the material in Dio's history may have come from Artorius directly.

Identification with King Arthur The possibility of Artorius as Arthur was first suggested by Kemp Malone in 1924. Although Artorius was not contemporaneous with the Saxon invasions of Britain in the 5th century, it is possible that he was remembered in local tales and legends that grew in the retelling.

Artorius is identified with King Arthur in the 2004 movie King Arthur (which moved him forwards 300 years to become a contemporary of the Saxons) and the 2005 PC game Barbarian Invasion.