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The triquetra is too similar to the symbol of the Sylvan faction. In fact, they are almost the same.

In Heroes of Might and Magic I, the Sylvan faction's symbol was a leaf.
The icon of a faction displayed above a town is one thing. The official symbol of the faction within the Ashan universe is another. In my humble opinion, it's best to avoid duplicates, although this depends on how closely you want to adhere to the established lore.
Faction Sketch
Goddess: Chimera
Country: Name unknown, known as the "Chimera Magi"
Capital: Morok
Symbol: Skull
Main colors: green, yellow
Lord: Letos
Main magic: Darkness, Chaos
Class: Inquisitor (in a distorted sense)
Army:
1. Undead/Restless/Decaying Undead
2. Harpies/Furies/Raiders
3. Chimera Guardians/???/???*
4. Centaurs/Centaur Captains/Centaur Rogues
5. Warlocks/Sorcerers - based on Druids
6. Minotaurs/Minotaur Guardians/??? - 2x2
7. Monster/Ancient Monster/???
* Chimera Guardians - approximate image - https://ubistatic-a.akamaihd.net/0004/prod/images/units/academy/academy_faction_art.png
City - redesigned Elven city]
If your mod involves replacing all cities (including those of the Sylvan faction) and you don't intend to adhere to the lore of Ashan, then please feel free to use this symbol as you wish; otherwise, THIS IS PURELY AN ELVEN SYMBOL, and there's no need to copy it.