Romans:
Officer's Quarters
Can only be built in the capital. At level 10, you can upgrade your Praetorians to Centurions. This is a one time upgrade and lasts for the game round.
Centurions gain strength in numbers. For every 100 Centurions trained in a village, their defence is increased by 0.05%. The bonus is maximised at +5% strength if you have 10,000+ Centurions trained in a village.
Additionally, you can use the Officer's Quarters to host Military Parades. These Parades boost morale, and for 24 hours, Centurions move at 9 fields/hour. However, they will become exhausted, and move at only 3 fields/hour for the following 24 hours. You can throw Military Parades in any number of your villages; you use the Officer's Quarters to select which ones.
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Lv1 to Lv9 - No effect
Lv10 - Option available to upgrade Praetorians to Centurions
Lv10 - Option available to host Military Parades
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Lv1 rough cost
500 wood, 650 clay, 850 iron, 250 crop
40 minutes to build
4 culture
Lv10 rough cost
48000 wood, 60000 clay, 82000 iron, 22000 crop
120 culture