Each level gives access to a bonus for cavalry troops. Ex: lvl 4 arena gives access to the lvl 4 upgrade bonus for atack or defense. Each level of the bonus gives 1-2% extra atac or defense for the troops made in that city, depending on the civilization.
Levels: 20
Requirements: Stables lvl 1
Costs:
- Wood: 380
- Iron: 310
- Stone: 450
- Gold: 140