Originally posted by Gobi Bear
Here is a quick explanation of the Plague in the Middle Ages scenario.
Start by looking at the ''4 Middle Ages.BIQ'' file in the editor and look at the Disasters! tab in the Scenario Properties dialog.
It lists:
''Earliest Start = 1346'' ... means that the AVERAGE date it starts in 1346 AD (the historical date)
''Variance = 50'' ... as explained in the editor online help, this is a measure of how variable the actual chosen start date is from 1346 AD.
''Duration = 50'' ... number of years plague will remain active ACROSS THE ENTIRE MAP (affecting all Civs) once it starts
''Strength = 100'' ... the Black Death in the Middle Ages scenario is set to be the strongest possible type of plague
''Grace Period = 100'' ... normally minimum number of years between plagues, but it is irrelevant in this case due to the next entry
''Max Occurrences = 1'' ... plague will never come back after its 50 year-run in this scenario.
Plague affects both units in cities and the population of cities.
It affects all players at the same time.
As I recall, the chance of a city contracting plague is determined by the level of trade going on in that city (harbors, resources, etc.), the size of the city, the strength of the plague, and whether or not there are walls.
Once a city has contracted plague, all you can do is wait it out (and move out the military units if possible).