He was the younger son of Gaius Julius Severus (b. ca 25), a Nobleman from Akmonia at Galatia, and paternal grandson of Artemidoros of the Trocmi, a Nobleman at Galatia, Asia Minor (son of Amyntas, Tetrarch of the Trocmi, King of Galatia), and his wife a Princess of the Tectosagii (daughter of Amyntas, Tetrarch of the Tectosagii).