Although Timothy Barnes has theorised that Justina was a granddaughter or great-granddaughter of Crispus through her unnamed mother (Crispus was the only son of Constantine I and Minervina), it seems more probable that she was in fact the granddaughter of Julius Constantius, son of Constantius Chlorus and half-brother of Constantine the Great. Justina's mother was probably a daughter of Julius Constantius and his first wife, the aforementioned Galla. Hence, this makes Justina at the heart of the family connexions between the Constantinian and the Valentinianic (and later Theodosian) dynasties.