Spires are creations of The Forgotten, designed to combat wizards. They were introduced in GemCraft Chapter 2: Chasing Shadows. They head towards the Orb, towering over everything, and are unbanishable (similar to Shadows from GemCraft: Labyrinth); the player will automatically lose if it reaches the Orb, since they will automatically destroy the Orb on contact. In GemCraft Lost Chapter: Frostborn Wrath, it was revealed that the Forgotten first created Spires during her last release (her 5th release, following her summoning). The Spires won thousands of battles for the Forgotten, killing thousands of wizards in the process, which allowed her to get dangerously close to the Spiritforge, before she was sealed away with the previous Gem of Eternity.
Generally, Spires have high, varying HP. Additionally, they have no armor, but their maximum damage taken per shot is capped (Max/HP), which makes Bolt or Barrage spells useless. However, the Beam spell and Poison gems are effective (as is Wake of Eternity). When they die, they destroy all nearby walls. Unlike Shadows, they move very slowly.
They spawn from edges that are farther away from the Orb, but that also means that if the Orb is in center of the field, it's vulnerable on all sides.
In GemCraft Chasing Shadows, they are first introduced in Vision Field V5. For players who skip over this level, Field O6 will mark their first encounter with a Spire. After beating O6, they'll appear occasionally every few battles in later fields, and at random every couple of battles on any field with "Flying Ones".
GemCraft Lost Chapter: Frostborn Wrath[]
They are introduced on Field E2. Afterward, they can appear at random on any field that has Flying Ones.