Of ancient and famous heritage, triremes are still very useful ships.
Senatores! While the armies of the Republic are invincible on land, our enemies hide on the seas! In addition to our huge Quinqueremes, the Republic needs smaller ships. The great Hellenic historian Thoukydides claims the first of these were built in Korinthian docks by the shipwright Ameinokles during their war with Korkyra (dates vary between late VIII and early VI century BC). At first they were rare, but as time passed more and more were built. In the great battles near Artemision and Salamis between Hellenes and barbaric Persians, Triereis formed the bulk of both fleets. Over time this class of ship became a bit obsolete, but they are still very efficient.
Unlike the other ancient ships, we know what Triereis looked like due to some very detailed reliefs and vase paintings. The only problem is that this info matches only the Greek variant. The Roman version could be simpler with only 2 rows of oars (manned 2-1) but we have no proof of this. The ship probably measured around 35x4.8m, which is the size of docks excavated in Peiraios. The ship had three rows of single manned oars on each side. Two lower rows (thalamioi - lowest and zygioi - middle level) were inside the hull, with the highest (thramitai) on open outriggers. Decks didn’t cover the whole width of the ship - probably only the hull width (some late Triereis are called kataphraktoi and this probably means that those had full decks). The crew consisted of 200 men, including 170 oarsmen (54 on both in-hull levels, 62 on the highest) and 30 officers, sailors and marines. We know that Athenian ships had 4 archers and 10 hoplites on board. Triereis were primarily designed for ramming attacks so they were very maneuverable at the cost of seaworthiness - in choppy sea they struggled. As mentioned the ram was the Triere's main weapon, but we assume that later full-deck versions carried additional marines or smaller ballistae. As with other ancient ships, Triereis had two sails for longer voyages - main on the central mast and another on the small foremast.