Temples are where you can use gold or crystals to purchase new units for your army.
Upgrading a Temple to higher levels opens up new units to buy. Units available in the next level of upgrade are shown darkened, and cannot be purchased until the Temple is upgraded.
Upgrade Levels
Level 1
Cost: Free.
Units: Dwarf Sharp Shooter
Level 2
Cost: 1,500 gold.
Units: Centaur Lancer
Level 3
Cost: 6,000 gold.
Units: Centaur Archer
Level 4
Cost: 15,000 gold.
Units: Warg Rider
Level 5
Cost: 28,500 gold.
Units: White Tiger, Fairy, Harpy, Great Wyrm, Tiger God