A fortress will make your empire more powerful in general and it will lessen the management and organisation that your realm needs. 

A  fully upgraded fortress will have the following enhancements: 

• higher bronze capacity (80.000)
• better exchange rates for silver and bronze
• higher capacity for wood, stone and ore (80.000 each)
• better base defence of the fortress wall (8.000)
• more available subjects (80.000)
• new offensive bonus in the barracks (+20% for each unit type)
• better resource production for wood, clay and ore
• a fortress is able to produce significantly more offensive or defensive power per hour in conjunction with its numerous offensive and defensive bonuses
• New runes
• New missions
• NEW UNITS!!!

But beware: The fortress is not as powerful as the individual villages were just after it has been created. It must be upgraded in order to achieve its true potential.

Attention: All active banners will be taken down when the villages are merged into a fortress.