Siege Attack

The biggest form of attack in the game, involving a larger part of a kingdom, including its forts.

The defender loses max 10% of his land (won Regular attack would give max 5%). The sieging attacker gains 1/3 of that, if the attacker was within 200% of defender net power before the battle (as in any attack).
To conquer the maximum amount of land in a siege attack, a sufficient number of units needs to have survived the battle to occupy each newly gained acre. The same goes to win forts. The number of units is 50 per acre taken, so an easy way to monitor if you have enough is to say 5 units per 1 acres of your opponent.
For eradication mages ('s only!), the enchantment Battle Chant makes that you also capture geld (like in a Pillage) after a won Siege.

Siege attacks are more difficult to win than regular attacks, because:

Since forts are involved, the targeted mage is granted defensive bonuses when defending.
On top of that, all Non-FLYING sieging army units receives a 10% accuracy penalty (base accuracy is 30%, in a Siege it becomes 20%, not taking the Siege unit ability into account).
However, the accuracy loss is disregarded on defending units with FLYING.
Examples:
- Exhibit A: A Chimera that sieges into a defending army WILL NOT suffer the 10% accuracy penalty
- Exhibit B: A Dark Elf Magician that sieges into a defending Dwarven Shaman WILL suffer the 10% accuracy penalty
- Exhibit C: A Dark Elf Magician that sieges into a defending Chimera WILL NOT suffer the 10% accuracy penalty
- Exhibit D: A Djinni that has suffered from the effects of Call Hurricane (and loses FLYING) that attacks into a defending Dwarven Shaman WILL suffer the 10% accuracy penalty
- Exhibit E: A Treant that has the benefit from the effects of Carpet of Flying that attacks into a defending Dwarven Shaman WILL NOT suffer the 10% accuracy penalty

Conditions for winning a Siege attack:

Outcomes for a Siege attack:

On Fort Damage Boost servers (Beta and Lightning), the defender will lose additional forts if the attacker is more than 200% NP of the defender (or vice versa) equal to the ratio between the Attacker/Defender's Mage Power (or vice versa)
On Fort Damage Boost servers (Beta and Lightning), the defender will lose additional forts if the attacker is affected by the defender's spell (or vice versa) equal to the ratio between the Attacker/Defender's Mage Power (or vice versa)
On the 7th Seal of Armageddon, the maximum amount of forts that can be destroyed in an attack is 20% of the defender's total forts
In no circumstance will a mage lose more than 75% of their forts in a single siege
The minimum amount of forts destroyed is equal to the total amount of land destroyed / defender's land pre battle
The number of forts destroyed is the nearest whole number rounded down from the land destroyed / defender's land pre battle
Mages who have Grand Conqueror 10 or greater gain 10% additional amount of barriers when barriers are capturable, and 3% additional all other building

Other Information:

A Siege takes 2 turns
A Siege can be blocked by Hallucination - the attacker loses 2 turns + war expense
The Battle Chant enchantment can give geld to a succesful invader of Eradication speciality.
Epidemics can be transferred from attacker to defender and from defender to attacker in Regulars.
Enchantments can be dispelled by Siege attacking, no matter if you win or not.
On the Beta Server, your army will not engage in battle with the opposing army if they are 20x stronger in total Power. This is the concept of preventing cheap scouting.