Often perceived as the poor relation of the army, the Roman Navy, in all of its various guises, whether Republican or Imperial, over the many centuries of its existence and in its disparate fleets, was in fact an extremely impressive and important force in its own right. At its height, it ruled the seas and the major river systems in and around Europe, Western Asia and North Africa; its squadrons ranged from the Black Sea to the Atlantic Ocean, from the north of Scotland to the western Sahara coastline. Not only that, but it exercised a power over those waters which was, for centuries, absolute; there simply were no other navies tolerated, a situation unknown by any other navy before, or indeed since.

It had not always been so, and the fleets had their ancestry in a few comparatively small and humble ships in the early fourth century BC, before growing to dominance by the mid-third century BC. This dominance was to last until the mid-third century AD, when a decline in strength, allied to increasing barbarian maritime activity from beyond the bounds of the Empire, started the process that would lead to its final extinction by the mid-fifth century AD. For approximately eight hundred years, therefore, hundreds and hundreds of Roman warships plied seas and rivers, evolving and changing all the while to meet different circumstances and the demands of a wide and changing variety of opponents and operating areas.

A warship is a complicated thing, and the building of a modern warship today, with all of its complexity, represents one of the highest expressions of technological ability. The same was also true two and a half millennia ago, pro rata to the technology of the day. Over the course of their long history, the Roman navies built, borrowed, adapted, invented and evolved a variety of warships for different tasks at different times and over a range of, and to suit, very different operational environments.

More than a thousand wrecks of ships from the period between the founding of Rome (753 BC) and the end of the Western Empire (AD 476) have so far been identified in the Mediterranean alone. However, with the exception of one or two fragments, no example of a seagoing Roman warship per se has yet been found.