I’ve wrote about the Earth seal a while ago, which give you the ability to turn a 15 farm fields city into a 18 farm fields city.

It cost your heart and soul though because you have to accumulate 10K of gold during the event.

Event 3: Magic Earth Seal Appears Again!!
If you accumulatively add 10000 gold in the deadline of the event, you will get Earth Seal X 1, Rotation Order, Level 3 * 1, Reforging Bolus * 1, Outpost Command * 2, Divine Recall X1, Enhanced Steel, Level 3 *1.

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More info about this event and other event here: http://forum.koramgame.com/thread-60075-1-1.html