But one surprise was balanced by another.

While the Roman labourers were constructing the mole, work was going forward night and day for two months in the Carthaginian harbour, without even the deserters being able to tell what were the designs of the besieged.

All of a sudden, just as the Romans had completed the bar across the entrance to the harbour, fifty Carthaginian triremes and a number of boats and skiffs sailed forth from that same harbour into the gulf--while the enemy were closing the old mouth of the harbour towards the south, the Carthaginians had by means of a canal formed in an easterly direction procured for themselves a new outlet, which owing to the depth of the sea at that spot could not possibly be closed.

Had the Carthaginians, instead of resting content with a mere demonstration, thrown themselves at once and resolutely on the half-dismantled and wholly unprepared Roman fleet, it must have been lost; when they returned on the third day to give the naval battle, they found the Romans in readiness.

The conflict came off without decisive result; but on their return the Carthaginian vessels so ran foul of each other in and before the entrance of the harbour, that the damage thus occasioned was equivalent to a defeat.