Polyreme

A Polyreme was a vessel with had more than three banks of oars. They progressed from ‘fours’, ‘fives’ and ‘sixes’ and eventually reached ‘sixteens’.
The Greeks developed Polyremes in competition with Carthage but they became obsolete after the Battle of Actium in 31 BCE.

The Polyremes became taller and taller and less and less manoeuvreable, but the bigger the vessel, the more prestigious was its owner.
They may have been used in conjunction with towers to besiege the sea walls of coastal cities because their decks were able to support catapults and marines in great numbers.

In 399 BCE, the first ‘four’ was constructed by Dionysius I of Syracuse according to Diodorus Siculus, probably in rivalry with Carthage who may already have built them.
Next came a ‘six’ under Dionysius II (367-344 BCE).
By 351 BCE Sidon had ‘fives’.
By 330 BCE Athens had 18 ‘fours’ and 392 ‘threes’.
By 324 BCE Athens had 43 ‘fours’ and 7 ‘fives’
By 315-314 BCE Antigonus I Monophthalmus, one of Alexander the Great‘s Generals from Macedonia, had 240 warships of which 210 were Cataphracts. He had 7 ‘threes’, 90 ‘fours’, 10 ‘fives’, 3 ‘nines’ and 10 ‘tens’. There were also ‘sixes’ and ‘sevens’.
By 301 BCE his son Demetrius I Polioretes had several ‘elevens’ and a ‘thirteen’.
By 288 BCE Demetrius had a ‘fifteen’ and a ‘sixteen’.
In 197 BCE Philip V of Macedon after being defeated by the Romans, was allowed to keep this ‘sixteen’. Livy describes this huge vessel as being difficult to manoeuvre. Three decades later, it was sailed up the Tiber by General Lucius Aemilius Paulus to celebrate his Roman Triumph over Macedonia.

Cataphract meant the vessel was enclosed by a deck for Catapults and Marines above the rowers. It might also have screens along the side to protect the oarsmen.
Most warships lasted between 25 to 30 years, before having to be replaced.