Chivalry is a Tier Three technology that can be researched after the Free Spirit tech.
It unlocks the Knight, a hard-hitting and fast unit that has "persist", a skill that allows the knight to attack again after killing a unit.
It also unlocks the Burn Forest ability, which allows you to transform forest tiles into field tiles with crop for 5 stars.
In the Aquarion Tech Tree, this technology is renamed "Spearing". Instead of unlocking the Knight, it unlocks the Tridention, a ranged swimming unit with dash and escape.