Fortresses play a key role during the Faction War and Invasion because they mark the territories owned by your faction.  Conquering a Fortress at the center of a region and holding it through the Contested Period will win ownership of the Region for your faction!

You must be part of a guild to initiate an attack on the fortress.
The fortress is initially owned by Skeletons and have skeleton defense buildings in them.
Once the fortress is conquered and owned by a Guild, the skeleton defense buildings will be replaced with high level defense buildings
The health of defense buildings in a fortress regenerate automatically after being destroyed
Once the health of the defense buildings restores back to around 50%, the defense buildings will participate battles.
If the owning guild is dismissed, the fort will be reset to its initial status, but the Skeletons will not be re-spawned which will make the fortress vulnerable.

IMPORTANT: If your city suffers a massive defeat in the region owned by an enemy faction, it will be teleported away to a random location!  This is not limited to the area of Lava Cracks! (This is activated when the War Zone fortresses open)

And if your city suffers a massive defeat on Lava Cracks (regardless the ownership of the region), it will always be teleported away to a random location. 

Fortress Bonus
Many players asked about adding bonuses to Fortresses. We are actively working on it, but also with great cautions, because excessive bonuses could make the strong stronger and the weak weaker. Therefore, we will gradually add perks for owning Temple/Fortress/Citadel in the future releases. Keep an eye on the News for more announcements!

Homeland Fortress
The Homeland Fortresses will play a key role during the faction invasion (2nd stage of the game). It marks the territory that your faction owns. At homeland, it represents which Guild/s have the leading position. Because the fortress' owner info is shown on the kingdom map, it will help the Guild to recruit or promote themselves if they own some fortresses.

Homeland Fortresses are protected by the Faction Border, which means enemy faction players are NOT able to attack the Fortresses in your homeland.

Owning fortresses also come with great responsibilities. When the faction war starts, the guilds who own fortresses will be the ones who responsible of defending the region they own against other factions.