COSTANZO I (Flavius Valerius Constantius), Roman emperor, surnamed CHLORUS. — Founder of the dynasty of the second Flavians, born in Illyricum, died at Eboracum (York) on 25 July 306. In 289 he was praetorian prefect under Maximian, whose stepdaughter Theodora he had married; by her he had six children, while from his natural union with Helena, who probably professed the Christian faith or inclined towards it, he had the future Constantine the Great. On 10 March 293 he was appointed Caesar in the tetrarchy established by Diocletian and solemnly adopted by his father-in-law; he received the diocese of Gaul as his part of the Empire to govern, in which he fought repeatedly against the Franks and Alemanni. When the persecution of Diocletian broke out, C. showed himself very lenient towards Christians, limiting himself to having a few churches demolished (cf. Lactantius, De mortibus persecutorum).
