The Merchant Convoy refers to a group of traveling merchants appearing in Fire Emblem: Path of Radiance and Fire Emblem: Radiant Dawn. It consists of a shopkeeper named Aimee, a weapon salesman named Muston, a weapon forger named Daniel, Jorge, who you can sell unneeded items to, and a Thunder Mage named Ilyana. Their native country is never revealed, as the character relations chart in Radiant Dawn displays them, as well as Volke, outside of any country.
Throughout both games, they travel with the player's army, and (with the exception of Ilyana who joins as a playable unit) offer their respective services from the Base, as well as managing the Supply Convoy.
In Path of Radiance, they make their first appearance in Gebal Castle at the beginning of Chapter 8: Despair and Hope. It is revealed they fled from Crimea into Gallia when Daein attacked, and all of them but Ilyana managed to make it safely to Gebal. They offer their services to Ike in return for their protection.
Ilyana, who got separated from the rest of the merchant convoy, was captured by Daein and is forced to fight the Greil Mercenaries during the same chapter. However, Ike can Talk to her and, by telling her about meeting the Merchant Convoy, convinces her to join them instead.
Throughout the rest of the game, the merchants will keep traveling with Ike, and provide him with their services. They also appear in a few Base Conversations throughout the game. In the epilogue, they take their leave of Ike and plan to travel to Daein.
In Radiant Dawn, Aimee and Ilyana first appear in Chapter 1-3: A Faint Light, where they, along with Kurth, are found in the same jail Micaiah was thrown in. Once Sothe rescues them, Ilyana joins your army, and once the chapter is finished, they are reunited with the rest of the convoy. They then decide to travel with Micaiah and provide her with their services for the rest of Part 1.
They re-appear in Chapter 3-2: Stormclouds, and bring along several units from Part 2. Apparently, Ike had contacted them and asked them for help. They then travel with Ike for the rest of Part 3. When Ashera's judgment turns everyone to stone at the end of Part 3, they are saved by being in the building where Yune awakened.
When the army splits up at the beginning of Part 4, Muston goes with Micaiah, Aimee goes with Ike, and Daniel and Jorge go with Tibarn. Which group Ilyana joins is up to the player. During Part 4, the merchants perform each other's tasks as well as their own, with the exception of forging, which can still only be done by Daniel. They also supply the player with powerful magic tomes, Rexbolt, Rexcalibur and Rexflame in various base conversations.