Apollo/Diana may unleash pestis at will. To impose pestis on a region, Apollo/Diana places the palus pestis (the fen of infirmity) near or on that region's banner. Only one pestis may occur at any time. Rome may not have a pestis placed on it during a hiems. An outbreak of pestis may not last longer than one year in any particular region.
Once pestis has been placed upon a region, all mortal players must flee that region. All provisions of movement during an aestas apply to players fleeing a pestis. Once Apollo/Diana has removed the pestis, players may return to the region.
War is the greatest plague that can afflict humanity, it destroys religion, it destroys states, it destroys families. Any scourge is preferable to it.