In the Smithy, you can forge weapons together to make them even more powerful! Forged Weapons will have a plus and a number next to the name to show how many times it has been forged. With each forging, the weapon will gain more Might and other boosts! You can also rename forged weapons and trade ores in for different ores here, if you find yourself in surplus of one type.
To forge a weapon, you must have the exact same copy of it. This means, to forge a +1 Iron Sword to a +2 Iron Sword, you must have another +1 Iron Sword to forge together with it. The cost of doing so are ores. Each weapon has a specific ore that is associated with it. With higher level forging, the ore cost will go up; however, this can be reduced if the character on smithing duty is proficient with that particular weapon. Some weapons cannot be forged (such as the divine weapons of the royal brothers), and any stave cannot be forged. If it cannot be forged, the game will tell you.
If you find yourself low on a specific type of ore, visit other players’ MyCastles or trade excess ores in for the ones you need! Note that you will have to trade 5 ores to get 1 different ore, and that you can only trade local ores. For example, you cannot trade 5 Rubies, a Nohrian ore, to get 1 Coral, a Hoshidan ore. Revelations will have access to all of them, though.
With forged weapons, you can name them into something different! While mostly for aesthetics and personal flair, there is one character that benefits from custom named weapons: Odin. If he is using a tome with a custom name at least 12 characters long, he gains a 10% critical chance boost! He is exclusive to Conquest and Revelations, so naming weapons in Birthright is for aesthetics only.