Crispus spent the following years assisting Constantine in the war against by then hostile Licinius. In 324, Constantine appointed Crispus as the commander of his fleet which left the port of Piraeus to confront Licinius' fleet. The subsequent Battle of the Hellespont was fought at the straits of Bosporus. The 200 ships under the command of Crispus managed to decisively defeat the enemy forces, which were at least double in number. Thus Crispus achieved his most important and difficult victory which further established his reputation as a brilliant general.