Heresy

Heresy is a technology available in Age of Empires II: The Conquerors as one of the new additions to the game accompanying that expansion pack.

Heresy is available on the Imperial Age, researched from the Monastery at a cost of 1000 gold. This technology is incredibly useful, as it prevents enemy monks from converting any of your units. When an enemy monk is converting one of your units, instead of it being transferred to the opposing team, the unit merely dies when converted. This means that your opponent will no longer be able use your units in battle.