Description (Gameplay)[]
Caelum is a nation of weak troops and strong mages, all with high mobility (since nearly everything flies). They have excellent access to Air magic, lesser access to Death, and minor access to Fire, Earth, and Water. Many of their troops resist cold and have extra Protection in cold.
They have two lines of national summons based on the good and evil spirits in Zoroastrian mythology. The good line requires Astral, which the evil line requires Death with a Fire crosspath; neither is accessible to any recruitable Caelum mage, so if you want access to these, you will need to create a pretender with S, D/F, or both. The commander summons in both lines are mages who provide an excellent and useful selection of paths.
Strategy[]
Caelum's national troops are weak, with only the Raptor Tribe being all that strong in melee. They make reasonable raiders thanks to their flight, but are not going to hold up to other nations' troops in melee. They do have access to Mammoths for expansion, which helps.
Their sacred troops are not particularly powerful, although they may be useful in a pinch.
Caelum's real strength is in its mages. The capital-only Eagle Kings have a guaranteed A4E1W1, allowing them to cast almost the entire suite of powerful Air battlefield spells like Fog Warriors, cast Living Clouds, or spam Thunderstrike. They also have Awe, allowing them to serve as semi-thugs in a pinch, but are more useful as casters supporting the troops.
After Storm and Stormpower are cast, the fort-recruit A2W1 Airya Seraphs can all cast Thunderstrike, one of the premier evocations in the game; even the 45g lab-rat A1 Spire Horn Seraphs can cast Lightning Bolt. They can thus field a frightening amount of flying mapmove 3 evocation artillery, and must use this to compensate for the weak troops.
Since most casualties will be caused by Thunderstrike cast by low-HP mages, Caelum must take extreme care around B9-blessed armies; against these you should ensure you have an Antimagic caster and Magic Resistance equipment on key mages.
The national summons provide crucial magic diversity, and will ultimately get you to a high level in all paths. Most of them are random, so generally you will need to make use of what you get. Their magic is some of the slowest to develop in the game, since their big summonable mages require Astral and Death gems, and you can't even search in Astral without indies or a pretender.
Caelum can field armies with all magic weapons (Spire Horn or Airya tribe troops), making Stygian Rains a powerful spell (castable by a Daeva of Frost and Snow, if you get one).
The key research is Evocation (for Thunderstrike and Storm), Conjuration (for Storm Power and the national summons), and Alteration (for Fog Warriors).