Final answer:
Christianity used hierarchical diffusion by converting rulers and influential figures, who then promoted it as the official religion of their realm, filtering down to the masses.
Step-by-step explanation:
Christianity used hierarchical diffusion as a way to spread its influence. This type of diffusion occurs when rulers or other influential figures convert to the religion and promote it as the official religion of their realm. As the religion filters down the political chain of command, it eventually reaches the masses. An example of hierarchical diffusion in Christianity can be seen when Emperor Constantine converted to Christianity and made it the official religion of the Roman Empire. This act greatly contributed to the spread of Christianity throughout the empire and beyond.