Flavius Julius Crispus (; c. 303 – 326) was the eldest son of the Roman emperor Constantine the Great and his junior emperor ("caesar") from March 317 until his execution by his father in 326. The grandson of the "augustus" Constantius I, Crispus was the elder half-brother of the future "augustus" Constantine II and became co-"caesar" with him and with his cousin Licinius II at Serdica, part of the settlement ending the Cibalensean War between Constantine and his father's rival Licinius I. Crispus ruled from Augusta Treverorum (Trier) in Roman Gaul between 318 and 323 and defeated the navy of Licinius I at the Battle of the Hellespont in 324, which with the land Battle of Chrysopolis won by Constantine forced the resignation of Licinius and his son, leaving Constantine the sole "augustus" and the Constantinian dynasty in control of the entire empire. It is unclear what was legal status of the relationship Crispus's mother Minervina had with Constantine; Crispus may have been an illegitimate son.