Chain Mail is a group of technologies in Age of Empires. All are researched in the Iron Age, at the Storage Pit.
Chain Mail Cavalry
Chain Mail Cavalry costs 175 food, and 100 gold, and increases cavalry armor by another 2.
This technology is required in order to upgrade to Heavy Horse Archer.
Chain Mail Archers
Chain Mail Archers costs 150 food, and 100 gold, and increases archer armour by another 2.
Chain Mail Infantry
Chain Mail Infantry costs 125 food, and 100 gold, and increases infantry armour by another 2.