Required units per battleround:
Normal Worlds / Normal Region Worlds: 12,500 units are required on each side (attacker, defender)
OLD Battle Worlds (Battle AS, EU, US): 50,000 units are required on each side (attacker, defender)
Other Battle Worlds: 25,000 units are required on each side (attacker, defender)
Conquer costs:
Conquering a metropolis costs 3 times the amount of silver that a regular city would cost.
When calculating the amount of silver a player needs to conquer another castle/fortress/city/metropolis, any metropolis that a player owns is counted as 75 individual castles