Codex Theodosianus 3.14.1, issued in the early 370s, has been understood in the past to indicate a ban on all marriages between ‘Romans’ and ‘barbarians’. But this interpretation contradicts evidence that Roman-barbarian marriages occurred with great frequency, and the lack of any other evidence for such a ban. This study argues that the specific wording of the law, referring to gentiles (barbarian soldiers) and provinciales (residents of provinces), suggests that the ban was imposed to ensure the continued performance of specific duties incumbent upon these two classes of individuals, and had nothing to do with ethnicity-qua-ethnicity.