Hellenistic-era warships

From the 4th century BC on, new types of oared warships appeared in the Mediterranean Sea, superseding the trireme and transforming naval warfare. Ships became increasingly large and heavy, including some of the largest wooden ships hitherto constructed. These developments were spearheaded in the Hellenistic Near East, but also to a large extent shared by the naval powers of the Western Mediterranean, specifically Carthage and the Roman Republic. While the wealthy successor kingdoms in the East built huge warships ("polyremes"), Carthage and Rome, in the intense naval antagonism during the Punic Wars, relied mostly on medium-sized vessels. At the same time, smaller naval powers employed an array of small and fast craft, which were also used by the ubiquitous pirates. Following the establishment of complete Roman hegemony in the Mediterranean after the Battle of Actium, the nascent Roman Empire faced no major naval threats. In the 1st century AD, the larger warships were retained only as flagships and were gradually supplanted by the light liburnians until, by Late Antiquity, the knowledge of their construction had been lost.

Most of the warships of the era were distinguished by their names, which were compounds of a number and a suffix. Thus the English term quinquereme derives from Latin quīnquerēmis and has the Greek equivalent πεντήρης (pentḗrēs). Both are compounds featuring a prefix meaning "five": Latin quīnque, ancient Greek πέντε (pénte). The Roman suffix is from rēmus, "oar": hence "five-oar". As the vessel cannot have had only five oars, the word must be a figure of speech meaning something else. There are a number of possibilities. The -ηρης occurs only in suffix form, deriving from ἐρέσσω (eréssō), "(I) row". As "rower" is ἐρέτης (erétēs) and "oar" is ἐρετμόν (eretmón), -ērēs does not mean either of those but, being based on the verb, must mean "rowing". This meaning is no clearer than the Latin. Whatever the "five-oar" or the "five-row" originally meant was lost with knowledge of the construction, and is, from the 5th century on, a hotly debated issue. For the history of the interpretation efforts and current scholarly consensus, see below.

In the great wars of the 5th century BC, such as the Persian Wars and the Peloponnesian War, the trireme was the heaviest type of warship used by the Mediterranean navies. The trireme (Greek: τρῐήρης (triḗrēs), "three-oared") was propelled by three banks of oars, with one oarsman each. During the early 4th century BC, however, variants of the trireme design began to appear: invention of the quinquereme (Gk.: πεντήρης (pentḗrēs), "five-oared") and the hexareme (Gk. hexērēs, "six-oared") is credited by the historian Diodorus Siculus to the tyrant Dionysius I of Syracuse, while the quadrireme (Gk. tetrērēs, "four-oared") was credited by Aristotle to the Carthaginians.

Far less is known with certainty about the construction and appearance of these ships than about the trireme. Literary evidence is fragmentary and highly selective, and pictorial evidence unclear. The fact that the trireme had three levels of oars (trikrotos naus) led medieval historians, long after the specifics of their construction had been lost, to speculate that the design of the "four", the "five" and the other later ships would proceed logically, i.e. that the quadrireme would have four rows of oars, the quinquereme five, etc. However, the eventual appearance of bigger polyremes ("sixes" and later "sevens", "eights", "nines", "tens", and even a massive "forty"), made this theory implausible. Consequently, during the Renaissance and until the 19th century, it came to be believed that the rowing system of the trireme and its descendants was similar to the alla sensile system of the contemporary galleys, comprising multiple oars on each level, rowed by one oarsman each. 20th-century scholarship disproved that theory, and established that the ancient warships were rowed at different levels, with three providing the maximum practical limit. The higher numbers of the "fours", "fives", etc. were therefore interpreted as reflecting the number of files of oarsmen on each side of the ship, and not an increased number of rows of oars.

The most common theory on the arrangement of oarsmen in the new ship types is that of "double-banking", i.e., that the quadrireme was derived from a bireme (warship with two rows of oars) by placing two oarsmen on each oar, the quinquereme from a trireme by placing two oarsmen on the two uppermost levels (the thranitai and zygitai, according to Greek terminology), and the later hexareme by placing two rowers on every level. Other interpretations of the quinquereme include a bireme warship with three and two oarsmen on the upper and lower oar banks, or even a monoreme (warship with a single level of oars) with five oarsmen. The "double-banking" theory is supported by the fact that the 4th-century quinqueremes were housed in the same ship sheds as the triremes, and must therefore have had similar width (c. 16 feet (4.9 m)), which fits with the idea of an evolutionary progression from the one type to the other.

The reasons for the evolution of the polyremes are not very clear. The most often forwarded argument is one of lack of skilled manpower: the trireme was essentially a ship built for ramming, and successful ramming tactics depended chiefly on the constant maintenance of a highly trained oar crew, something which few states aside from Athens with its radical democracy had the funds or the social structure to do. Using multiple oarsmen reduced the number of such highly trained men needed in each crew: only the rower at the tip of the oar had to be sufficiently trained, and he could then lead the others, who simply provided additional motive power. This system was also in use in Renaissance galleys, but jars with the evidence of ancient crews continuing to be thoroughly trained by their commanders. The increased number of oarsmen also required a broader hull, which on the one hand reduced the ships' speed, but on the other offered several advantages: larger vessels could be strengthened to better withstand ramming, while the wider hull increased their carrying capacity, allowing more marines, and eventually catapults, to be carried along. The decks of these ships were also higher above the waterline, while their increased beam afforded them extra stability, making them superior missile platforms. This was an important fact in an age where naval engagements were increasingly decided not by ramming but by less technically demanding boarding actions. It has even been suggested by Lionel Casson that the quinqueremes used by the Romans in the Punic Wars of the 3rd century were of the monoreme design (i.e., with one level and five rowers on each oar), being thus able to carry the large contingent of 120 marines attested for the Battle of Ecnomus.

An evolution to larger ships was also desirable because they were better able to survive a bow-on-bow ramming engagement, which allowed for increased tactical flexibility over the older, smaller ships which were limited to broad-side ramming. Once bigger ships had become common, they proved their usefulness in siege operations against coastal cities, such as the siege of Tyre by Alexander the Great, as well as numerous siege operations carried out by his successors, such as the siege of Rhodes by Demetrius Poliorcetes.

There were two chief design traditions in the Mediterranean, the Greek and the Punic (Phoenician/Carthaginian) one, which was later copied by the Romans. As exemplified in the trireme, the Greeks used to project the upper level of oars through an outrigger (parexeiresia), while the later Punic tradition heightened the ship, and had all three tiers of oars projecting directly from the side hull.