Glyph of Fortification

The Glyph of Fortification, commonly shortened to Glyph, is an ability activatable by any player on a team that causes all friendly buildings to recieve a massive armor bonus and magic immunity for effective invulnerability to almost all sources of incoming damage. The effect has a short 5 second duration with a 5 minute cooldown.

Mechanics
The Glyph of Fortification can be activated by any player on a team by a small icon in the bottom right corner of the screen as long as it is off cool down. When activated, it grants a massive impenetrable armor bonus to all buildings belonging to that team, including towers, barracks, and the Ancient, making them immune any source of incoming damage.

Despite being invulnerable to damage, units can still perform the action of attacking or targeting buildings under the effects of the Glyph.

Trivia

 * The visual effect used by the Glyph of Fortification is identical to that used by Black King Bar's Avatar ability.
 * In earlier versions of DotA, Glyph did not grant magic immunity, and skills such as Pugna's Nether Blast could attack through the invulnerability.