Soon after this event, we are furnished with materials, from which we may judge of the comparative opulence, commerce, and shipping of the several countries which bordered on the Mediterranean.  Constantine and Licinius were contending for the Roman empire; and as the contest mainly depended on superiority at sea, each exerted himself to the utmost to fit out a formidable and numerous fleet.  Licinius was emperor of the east:  his fleet consisted of 380 gallies, of three ranks of oars; eighty were furnished by Egypt, eighty by Phoenicia, sixty by Ionia and Doria, thirty by Cyprus, twenty by Caria, thirty by Bithynia, and fifty by Africa.  At this period there seems to have been no vessels larger than triremes.  The naval preparations of Constantine were in every respect inferior to those of his rival:  he seems to have got no ships from Italy:  indeed, the fleets which Augustus had ordered to be permanently kept up at Misenum and Ravenna, were no longer in existence.  Greece supplied the most if not all Constantine’s vessels:  the maritime cities of this country sent their respective quotas to the Piraeus; and their united forces only amounted to 200 small vessels.  This was a feeble armament compared with the numerous and powerful fleets that Athens equipped and maintained during the Peloponnesian war.  While this republic was mistress of the sea, her fleet consisted of 300, and afterwards of 400 gallies, of three ranks of oars, all ready, in every respect, for immediate service.  The scene of the naval battle between Licinius and Constantine was in the vicinity of Byzantium:  as this city was in possession of the former, Constantine gave positive orders to force the passage of the Hellespont:  the battle lasted two days, and terminated in the complete defeat of Licinius.  Shortly after this decisive victory, the Roman world was again united under one emperor, and the imperial residence and seat of government was fixed by Constantine at Byzantium, which thenceforth obtained the name of Constantinople.

In the middle of the fourth century Ammianus Marcellinus gives us some important and curious information respecting the Roman commerce with the East.  According to him it was customary to hold an annual fair at Batnae, a town to the east of Antioch, not far from the banks of the Euphrates.  Merchandize from the East was brought hither overland by caravans, as well as up the Euphrates; and its value at this fair was so great, that the Persians made an attempt to plunder it.  To the same author we are indebted for some notices respecting the countries which lay beyond the eastern limits of the Roman empire, and also for the first clear and undoubted notice of rhubarb, as an extensive article of commerce for medicinal purposes.

Towards the end of the fourth century, the naval expeditions of the Saxons attracted the notice and excited the fears of the Britons and the Gauls:  their vessels apparently were unfit for a long voyage, or for encountering either the dangers of the sea or of battle; they were flat-bottomed and slightly constructed of timber, wicker-work, and hides; but such vessels possessed advantages, which to the Saxons more than compensated for their defects:  they drew so little water that they could proceed 100 miles up the great rivers; and they could easily and conveniently be carried on waggons from one river to another.