Were ancient war-galley rowers slaves or professionals?

Were ancient war-galley rowers enslaved laborers or paid professionals?

Effective crews were generally paid, trained professionals because coordinated combat rowing demanded skill, fitness, and motivation.

The exchange rejects the familiar image of an effective war galley powered mainly by starved slaves. Warships needed paid and trained rowers who could synchronize several banks of oars under combat conditions. A quinquereme's arrangement could place several people within each bank, making timing and physical conditioning as important as raw strength. Because merchant shipping also employed rowers, skilled oarsmen could find work in peace as well as war and had strong reasons to preserve the vessel they served.