Envoys are much more useful as sources of diplomatic influence with city-states. This utility, however, comes with increased cost. Players will need ample Paper, either through trade or the building of Chanceries, to supply the demand of their burgeoning diplomatic service. City-state quests are still very important for maintaining friendly or allied relations, however their importance is waning.
During the Medieval period, the art of diplomacy finally came of age. New theories on foreign affairs emerged during this time that were no longer based on 'might is right,' but rather the arts of flattery, sophistication and, if necessary, intimidation. The Envoy represents this leap in diplomatic power and, as such, is both more effective than Emissaries and also more expensive.