The Mansion allows you to produce Silver in your City. It also increases the maximum amount of Silver that is protected from your enemies. This building is essential for increasing your Capitol's level.
You can build a Mansion right after you finish the game tutorial.
Click on any small tile you wish to place the building on.
Next, select the Mansion icon.
You can demolish this building by following the instructions in this article.

Silver is one of the most important currencies in the Kingdom. It can be converted into Scientific Tractates by Clan Universities and is also used to kick out unwanted players from a Clan's territory. In addition, Silver can be used to train troops and purchase mercenaries during the "Trade Routes" tournament. Finally, Silver can be used to revive troops.