The "Ancients’ Protection" is a strong army whose vocation is to assist game beginners. It’s better not to attack such cities.
Every player can receive Protection of the Ancients as reward for several quests.
In order to complete the very first quest with the Ancients’ Protection reward you will need to open the City Gate. Consider that Ancients’ Army will arrive in 3 hours after the reward has been accepted.
The Ancients will stay at your Assistant Slots for 60 days on Mining and Tactical Servers.
If a player doesn’t log into the game for more than 8 days, the Ancients will leave sooner.