Roman oarsmen were paid auxiliaries rather than slaves. A ship depended on them for propulsion, making rebellion during an enemy boarding a direct threat. Limited space also restricted the number of additional soldiers a vessel could carry. Sending troops ashore for reconnaissance could otherwise leave only a few men guarding dozens of strong rowers. Paid crews avoided the internal security problem that an enslaved rowing force would create.
Notable Point · 30:49-32:05
Why paid Roman oarsmen mattered when troops went ashore
Paid auxiliary crews helped Roman river vessels send troops ashore without leaving a small guard to control enslaved rowers.