Noticed when fighting in marsh areas.
Sending native units to fight the Menapii and defeating them. Chasing down routed units and then enslaving them. Problem with this? Slaves get stuck.
Slaves could probably use the flooded marsh movement trait, otherwise you end up with multiple groups stuck on the map that you can't use. Unlike Caesar I have no intention of letting them run home to refill the recruit pool for the next 'rebellion' and I'd prefer if I didn't have to execute useful bodies.