Sébastien Castalion (kăstāl´yən, kăstĕl´yō), 1515–63, French Protestant theologian. Castalion was with Calvin at Strasbourg and Geneva until he split with Calvin over doctrinal differences and moved to Basel. He obtained a chair of Greek literature in the university there. In the preface to his Latin translation of the Bible (1551) Castalion defended religious toleration. In 1554 he published, under the pseudonym Martinus Bellius, Concerning Heretics (tr. 1935), in which he protested the execution of Servetus. The name also appears as Castellion and Châtillon.

See S. Zweig, Right to Heresy (1936).

Sébastien Castellio: see Castalion, Sébastien.