Grapeshot

[kronckew]

Yup, that's pretty much it, tho your image makes it look like a bit smaller than it probably was. It was more of an ungainly & heavy bridge with decking and railings to carry a section of Roman Marines in Armour charging across, and was pivoted so it could swing out to the sides as well as fore/aft. breaking loose in a storm would make the narrow warship disastrously unstable. The trireme while looking substantial was rather light and fragile so that it could be rowed for fairly long distances in battle. unlike the movies, they were manned by free men, sailors and Marines of the Roman Navy. The use of slaves and prisoners was a more recent late renaissance thing, the Venetian, Spanish and Turkish galleys were famous for their unpleasant aroma as the slaves were chained to the benches and there were no toilet or bathing facilities.

[fernando]

Originally Posted by kronckew

...Yup, that's pretty much it, tho your image makes it look like a bit smaller than it probably was...

I just picked that one as i could pick another. Meaning to say that images, even those carved not far from or even within the period may, or in fact, are less an evidence of facts than the author's imagination.
If you take the trireme, you then ought to acknowledge that there also were Mediterrnic monorremes, birremes, quadriremes and quinquerremes. Taking into consideration the presumption that each line of rowers of would need a different deck, imagine one of these ships with such a multi deck construction or, how long would the oars in the upper deck have to be to submerge into the water, besides considering that the different decks should have a reasonable distance between each other, to prevent the oars from getting tangled. A realistic reasoning is that what happened is that, there was only one row of oars, where two to five men would operate one oar, having inside the ship a number of pavements with different heights, with seats inclined towards aft ship, the lower one the thalamite, then the 'sigite', 'tranite' etc.

[fernando]

Originally Posted by kronckew

... unlike the movies, they were manned by free men, sailors and Marines of the Roman Navy...

Basically, yes. What a temptation would be to draft the losers from a battle towards such a captive entertainment ... salary savings diving into the captain's purse .