"The Treasure Chamber keeps your riches. It is a golden sea of joy. By upgrading the Treasure Chamber you can store even more of your Gold you bring home from your conquests."
The Treasure Chamber is where a player's available gold is stored. All gold from raids, chests, and item sales is collected there. When the chamber's capacity is reached, no more gold can be accumulated.
Gold from taverns is transferred to the Treasure Chamber only when it's collected. If there's no room for it, it is simply not collected.
Whenever other players raid a kingdom, they may steal some gold. This gold either comes from the Treasure Chamber, or from taverns. A certain amount of gold in the chamber is protected whereas taverns are unprotected. The protected amount in the chamber increases with its level.
Inside the chamber, players can activate the gold shield to protect all of their gold (including tavern reserves) from raids for a limited time.