How to Move Your Main Castle
You can relocate your main castle to a different spot in the Empire. The move takes 24 hours, can't be canceled, and while it's underway you can't attack or send resources from that castle.
Where You Start the Move
In the castle management menu you pick a new location. It can be an empty castle spot, or a ruin, for which the game shows exactly when it will be cleared and the spot freed up. Once you confirm, a countdown starts and the castle relocates on its own.
What the Move Means
The move takes 24 hours. During that time you can't attack or send resources from the castle, the action can't be canceled, and you can't start it while you have troops, scouts or trade carts out. Outposts don't move with it, they stay where they are, so after the move your castle might end up far from your own outposts.
How Much It Costs
After a friend invites you, the first move to their location is free, every following move costs rubies. The game shows the price and the remaining time before you confirm, so you can think it over.
When Moving Is Actually Worth It
It mainly makes sense when you want to get closer to the alliance you play with, or to get away from a neighborhood that keeps raiding you. Moving just to get better robber baron camps nearby isn't worth it though, since they respawn on the map and their level scales with yours.