Bulgarians: Initially, the team bonus makes Chain Mail Armor research 50% faster. With the update, Chain Mail Armor is researched 80% faster. Chain Mail Armor costs -50% food.
Portuguese: Chain Mail Armor is researched 30% faster as a civilization bonus.
Armor made of linked metal chains was an improvement over a cascade of metal scales. It had greater intergrity and held up better after taking some damage. Whereas a row of scales might come loose after a blow, chain mail armor stayed largely intact. Because the linked chains were smaller than the scales they replaced, chain mail armor was more flexible and comfortable to wear. While an improvement, chain mail armor was also more expensive and time-consuming to manufacture.
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—Age of Empires II manual
Trivia[]
Since the word "mail" in the context of armor properly refers only to the type of armor that consists of small metal rings linked together, the names of the other infantry armor technologies are contradictory, while the name of this technology is arguably redundant.