A Historical City (or HC) is a special city on Evony Age 2 which starts at level 12, then 14, then 16, and finally 18. Atlantis is the only level 18 HC, and each HC can have resource fields up to their level. For example, a level 12 HC will start with 1 of each resource field at level 12, and every other can be upgraded to level 12. However you only need a Mich Script for level 10.
Each Historical City is granted powers on a radius around them, Atlantis, however, can affect any city on the map. For this reason, many players consider owning Atlantis game-ending, since the player controlling Atlantis can send a lot of troops out, and can take troops from any city in the server.