Glyph of Fortification

The Glyph of Fortification, or Glyph, is an ability usable by any player that causes all friendly buildings to become impervious to damage for a short duration. Glyph lasts for five seconds, and has a five-minute cooldown per team. A team's Glyph cooldown is instantly refreshed when they lose a Tier 1 tower.

Mechanics
The Glyph of Fortification can be activated by any player with a button in the bottom right corner of the screen. Glyph grants spell immunity and a massive impenetrable armor bonus to all buildings belonging to that team, making them immune to any source of incoming damage. Despite being invulnerable, units can still perform the action of attacking or targeting buildings under the effects of the Glyph.

Trivia

 * In earlier versions of DotA, Glyph did not grant spell immunity, and skills such as Pugna's Nether Blast could attack through the Glyph.
 * In DotA, Glyph grants friendly buildings +9999 Armor instead of causing them to become invulnerable.