Ribannah
Fighter Druid
Pilferman: no secret. 
I just sent the one Archer out to catch me some Slaves and maybe get a good peace deal, and found Carthage with Bronze Working discovered but no Mercs built yet, so I took the opportunity. Once healed I sent him out again for the same purpose and found a very backward France. Really too far away to be a great asset to the empire, but the room it gave me - basically controlling almost the entire north part of the map - was significant.
But you have to send out that Archer in the first place to be able to find such an opportunity.
In hindsight, I should perhaps have sent an Archer southeast, too, instead of a Warrior, with a chance of taking out a civ (Rome) there as well. They had excellent real-estate!

I just sent the one Archer out to catch me some Slaves and maybe get a good peace deal, and found Carthage with Bronze Working discovered but no Mercs built yet, so I took the opportunity. Once healed I sent him out again for the same purpose and found a very backward France. Really too far away to be a great asset to the empire, but the room it gave me - basically controlling almost the entire north part of the map - was significant.
But you have to send out that Archer in the first place to be able to find such an opportunity.
In hindsight, I should perhaps have sent an Archer southeast, too, instead of a Warrior, with a chance of taking out a civ (Rome) there as well. They had excellent real-estate!