Priests are a very important unit to the human army if you want to keep losses to a minimum, the low health of your frontline units makes it hard to beat others without major losses, priests can double your unit’s health via all their healing. Priests also provide any unit immunity to poison damage for a few seconds which greatly helps when fighting against spiders.

Priests counter undead units once they are Silver tier or higher, they gain an AoE spell that does high damage to all undead units, this is a very useful skill against Lich players.

Priests are very fragile and any unit can kill them easily but the Calvary charge and other burst damage is the best counter to priests.

Research for Priests is unlocked at academy level 3, you will likely be able to start researching for this unit before you even unlock this unit.

Tier 1: Fitness Training – Bonus +% health, leads to silver Priests.
Tier 2: Combat Training – Flat bonus to damage, leads to Smite, which adds a stun to the “Holy Blast” ability of the silver and gold priests. This is very powerful but will rarely be used outside of quests.
Tier 3: Restoration – Increase healing output by +%, leads to Detoxify, this research allows priests to remove poison effects from your units, this research is the most important research for priests, as it allows you to stand up against the lich unit known as the spider.
Tier 4: Basic Fitness Training – more +% health, leads to gold priests, gold priests are great as they have a target Mass Heal ability which works a lot like Vega’s heal ability but at a lower cost and is cast from a standard unit and not a hero.
Tier 5: Convalescence – reduced healing time always good, leads to reduced garrison healing time.
Tier 6: Advanced Fitness Training – more bonus +% health always good, leads to poison immunity, this research gives all units 7 seconds of immunity to poison when healed by “Mass Heal”
Tier 7: Garrison Training – increase health and damage while garrisoned. Leads to grassland training, +20% health and damage while fighting in grassland battlefields.
Tier 8: Training Discipline – Reduce cost to produce priests, leads to research that reduces the amount of crystal needed to produce priests by 20%
Tier 9: Elite Combat Training – more +% damage, I personally wish these damage bonus researches were bonus to healing but that is me. Leads to +20% damage research.
Tier 10: Advanced Convalescence – more reduced healing time, leads to even more garrison reduced healing time.
Tier 11: Advanced Restoration – increase healing output of priests by +%, leads to +20% attack speed research.
Tier 12: Elite Fitness training – more bonus +% health, leads to Regroup increasing the size of a troop of priests from 8 to 10.