Fortress

This is the symbol of your power, as well as defending place for your military. Without a fortress, you have no way to order your people to perform certain tasks. After losing your last fortress, you must start everything from the ashes.

Forts also give a bonus to the HP of your army on defense. A base HP bonus of 10% on regular attacks and 20% on siege attacks always applies. Investing more than 0.67% of kingdom land in forts makes the bonus increase linearly until a maximum bonus of 37.5% on regulars, and 75% on sieges, is obtained at 2.5% of kingdom land.

Forts add to your power, but only the first 2.5% of your land. (since May 2008)

Forts also provide a residential max increase of 500 pop (Residence only, no food)

A recommended ratio is 1% of your land in forts, as maxing out forts at 2.5% will make you look much stronger than you really are.

Upkeep

The upkeep of forts differs from that of other buildings in that each additional fort built has a higher upkeep than the last one. This means that building a large amount of forts can very quickly cause a significant increase in geld upkeep.

The upkeep U_n of the nth fort is:

U_n = 240 + 60n

It follows from this that the total upkeep U(n) for n forts is:

U(n) = 240n + 30n(n+1)

Past Usage

Following changes to oversummoning, Fort Halling was a decent way to gain power and rank during Armageddon. This is no longer the case because the Forts above 2.5% do not increase your power design change.