Flavius Julius Crispus (/ˈkrɪspəs/; c. 300 – 326) was the eldest son of the Roman emperor Constantine I, as well as his junior colleague (caesar) from March 317 until his execution by his father in 326.

After his elevation to imperial rank, at which point he was also entitled princeps iuventutis ("Prince of Youth"), the Latin rhetorician Nazarius composed a panegyric preserved in the Panegyrici Latini, which honoured Crispus's military victories over the Franks in c. 319.

According to the Latin histories of Ammianus Marcellinus and Aurelius Victor, after a trial whose real circumstances are mysterious, Constantine executed Crispus at Pola (Pula) in 326.

[3] By that time, his mother Minervina was either dead or set aside, as his father Constantine was married to Maximian’s daughter Fausta.

On 1 March 317, the two co-reigning augusti jointly proclaimed three new caesares: Crispus, alongside his younger half-brother Constantine II, and his first cousin Licinius Junior.

By October 322, Crispus was already married to a woman named Helena, as she bore him a child, a son Flavius, in that month.

He honoured his son for his support and success by depicting his face in imperial coins, statues, mosaics, cameos, etc.

The accounts of Zosimus and Zonaras say that Crispus was executed due to suspicions that he was involved in an illicit relationship with Fausta,[13] but some scholars have been skeptical of this explanation.

[14] While Hans Pohlsander considers Barnes’ argument to be invalid on the basis that Crispus was in the East for long enough,[15] he suggests that the similarity of Zosimus' story to the myth of Phaedra and Hippolytus makes its veracity doubtful.

According to his theory, Crispus was exiled to Pola as a punishment for his adultery and committed suicide by poison there, and Fausta's death was caused by an attempt to induce abortion to get rid of an unwanted pregnancy that resulted from her affair.