Any Coalition that conquers a Pantheon must defend it from increasingly powerful waves of Xerxes' Army. With each successful defensive battle against Persian units, your Coalition will receive Orichalcum for all Persian Units eliminated in the battle. This mineral can be used to grant "Veteran" status to your Units - reducing their Grain consumption, increasing their strength and improving their overall effectiveness in battles. All Orichalcum received for defeating Xerxes' Units will be delivered to the Pantheon where the battle took place, and can be accessed by any member of the Coalition that had Units participating in the battle.
Orichalcum can be moved between all Pantheons controlled by a single Coalition, but be aware that some may be lost due to theft and corruption in transit. The greater the distance between Pantheons, the more Orichalcum will be "lost" on the way.
Different Unit classes are able to be upgraded to Veteran status depending on each Pantheon's level of development. The higher the level, the more types of Units can be upgraded:
Level 2 - Light Infantry
Level 3 - Heavy Infantry
Level 4 - Phalanx Units
Level 5 - Cavalry.
Bear in mind - each Pantheon will be classified as a higher priority target for the Persian horde with each additional upgrade level, attracting larger forces to attack and retake it. Successful defense of Pantheons against larger forces will in turn provide you with more Orichalcum, with which you may create more Veteran Units. Developed Pantheons will also receive more Orichalcum for each Persian Unit killed, as well as a higher overall Defense Bonus.
The Coalition Hegemon and Polemarch are able to move Orichalcum between all Pantheons controlled by their Coalition. However, be aware that some may be lost in transit. The respective distance and development levels between different Pantheons will determine how much Orichalcum will be "lost" on the way.
To grant Veteran Status to your Units, send Units to one of your Coalition's Pantheons and open the "Veterancy" window. Select the number and type of Units you wish to upgrade to Veteran status and click "Upgrade". You can review the Pantheon's Unit upgrade history from the "Veterancy History" window in the Pantheon interface.