The series indicates that the rule against fighting on holy ground also applies to immortals fighting with mortals. On multiple occasions, Duncan finds a mortal enemy at a cemetery or crypt and feels duty bound not to attack them. This is treated as a rule of honor, similar to the first movie. In the episode "Little Tin God", the character Joe Dawson describes a legend that says the eruption of Mount Vesuvius was caused by "two Immortals going at it in a Temple of Apollo" in Pompeii, breaking the rule. However, he admits this is only a rumor with no evidence to back it up.