We have freed some slaves to hold our settlement until a more suitable force arrives. Pray they fight better in battle than what we've seen of them so far.
These men are slaves who have taken their freedom in a revolt, or have been freed by their native masters to secure their aid in one led by them. They will fight a perceived oppressor, but are untrained and carry minimal weaponry found at the time of revolt. They pick up stones to throw, which can be useful against unarmoured opponents, but don't expect them to do any wonders on the battlefield. They are inferior to every other unit, and particularly unsuitable for fighting cavalry.
They should be released from this temporary militia service to pursue a new life as free citizens as soon as the risk of retribution has passed and a more suitable garrison has been established.