Swamped

Well. You know how the Bogknights get to the swamp - in carriages.

And carriages have drivers.

"Can you drive a carriage?"

The man nods weakly.

"The group you'd be defending against has some members here on leave. If you're thinking of taking that side instead... they've got more ties to the outside. Not nearly as safe for someone like you. But what matters is, they'll be going back to the swamp soon. Find a way to get yourself driving their carriage. To get in touch with the fortress..."

You pause. You were about to tell him how to send a crow from one of the shelters outside the swamp, but this is many years in the past. Crows aren't in common use yet. You've got no idea how the Marshguards did things before them. And you can't exactly find one to ask.

So you'll need to give him some other option.