Since this unit is a Galley with slightly improved stats, the Bireme's main use is to both pillage enemy Trade Routes and naval tile improvements as well as provide protection for Phoenician trade rather than waging all-out wars just by using a group of Biremes themselves. On maps and regions with naval warfare emphasis, however, they can quickly reach and devastate unprotected coastal cities very early in the game.
As technology progresses and the Biremes lose their usefulness in combat and harassing enemies, they can still be kept around without upgrading to protect Phoenicia's much extended naval trade network.
A bireme is a rowed vessel with two banks of oars for rowers arranged in upper and lower decks and armed with a bow ram. The Phoenicians were the foremost shipbuilders of the ancient world and are generally credited by most archaeologists and historians with creating the bireme design, even though the word “bireme” is Latin. The Phoenicians were also perfectly willing to build warships for anyone with ready cash, whether the Greek city-states, or the Persians, or any other Mediterranean power.
Naval engagements in the ancient world consisted of trying to run down the other side's ships with a bronze-wrapped bow ram while avoiding being rammed in turn, or getting entangled in a sinking ship and being dragged to a watery doom. Ancient sources use adjectives like “chaotic” and “frenzied” and “terrifying” to describe these naval battles, which seems entirely justified. Archaeological evidence attests to a common practice of painting eyes on the bows of many ships to ward off evil.