The Dragon's Monument is a building affiliated with the Dragon Clan.
This intricately carved monument represents the pinnacle of the Dragon Clan's artistry, as well as the ultimate expression of its warriors' courage and faith. In the fearsome Ritual of Purity, four Samurai must disembowel themselves on the pedestals surrounding the Dragon. Simultaneously, they must recite the Clan's most ancient spell in a language spoken only for this purpose. Though the Ritual has not been performed in recorded history, it is believed capable of summoning the Dragon himself.
In-game, the Dragon's Monument has a purpose similar to a super-weapon; through sacrificing four Samurai and three points of Yang, the player can call forth a rain of fire at a target location that can easily wipe out an entire army of enemy troops.
There are limits to the ability of course; since four Samurai must be sacrificed, significant resources must be used up in training the troops themselves, and the sacrifice of three Yang energy points is not something to be taken lightly, as the points could instead be used for upgrades, summoning Ninjas/Monks or purchasing Zen Masters.
The Dragon's Spirit ability does not affect friendly troops, but neither does it do any damage to enemy structures.