Relics affect different attributes of your Units and Castle. Fight, claim, capture, and control Shrines to acquire new Relics. Build a Temple of War to store and use the Relics you find. Construct the Eagle's Nest and House of Lords to locate and capture different Shrines throughout the Map.
You can sell Relics you don't want to use for Resources. In order to do so, go to the Temple of War, select a Relic you would like to sell, and click the "Sell" button. Note that you cannot sell a temporary Relic that has been activated.
Relics can have several different kinds of attributes. Some offer Offensive bonuses, while others improve the Defensive attributes of various Units. Other Relics mainly improve the production performance characteristics for your entire Castle (Resource production, Defense bonuses, etc.)
To use a Relic, place it into any open Activation slot on the Altar at your Temple of War. You have 6 Activation Slots in total, and can use no more than two Relics of the same category simultaneously. For example: 2 Offensive Relics, 2 Defensive, 2 Production.
Relics are categorized as either as either Sacred or Infernal based on their relative strength and stability. Sacred Relics possess small, but stable powers. Infernal Relics have both strong positive and negative effects.
The strength of a Relic's attributes is measured in proportion to its rarity (Common, Noble, Royal, Imperial, and Divine). The harder it is to find, the stronger its effect.
Relics claimed in Battles
Fighting with other Castles or Settlements is one way to acquire new Relics. Your Grand Marshal will brief you on any Relics you have recovered following each Battle. If there is a blue highlighted exclamation point next to the report instead of the normal red one, it means you have claimed a new Relic!
Open the report and read the description of your prize in the top window. You have a chance to claim a new Relic regardless of the outcome of an engagement. Remember: In order to keep your new Relic you must go to your Temple of War and either use it immediately or move it to your Reliquary, or it will disappear in 48 hours. You can go there directly from your Grand Marshal's report.
Relics recovered from Shrines
Ring of Summoning, Crematorium, Fallen Cathedral, Sorcerer's Keep are where the Relics are concealed. They essentially function like a normal Settlement. Conquer one of them and control it for at least 1 hour to begin trying to salvage Relics. After the first hour, you can begin your search for the Relics by clicking the "Search" button.
The longer you occupy a Relic Settlement, the higher your chances of successfully recovering a Relic for each attempt. You are allowed one detecting attempt per hour. Once you've successfully recovered a Relic, you will receive a report from your Lord Steward. Remember: In order to keep your new Relic you must go to your Sanctuary and either use it immediately, or move in to your Reliquary or it will disappear in 48 hours - you can go there directly from the Lord Steward's report.