Glyph of Fortification

Glyph of Fortification, abbreviated as Glyph, is an ability usable by any player on a team and activated by a small icon in the bottom right corner of the screen. When used, all Buildings on that player's team become invulnerable to physical damage and receive Magic Immunity for 4 seconds. Glyph of Fortification has a 5 minute cooldown.

Mechanics
The Glyph of Fortification can be activated by any player on either team as long as it is off cooldown. When activated, all Buildings belonging to that team, including Towers, Barracks, and the Ancient, will be impervious to physical damage as well as most sources of magical damage. The Glyph lasts for 4 seconds and has a Cooldown of 5 minutes. Cooldown is shared between all players on a team, which means that if one player activates it, no other player may use the Glyph until the cooldown expires.

Despite being invulnerable to damage, Heroes and Creeps can still attack buildings under the effects of the Glyph.

Trivia

 * The effect used by the Glyph of Fortification is identical to that used by Black King Bar's Avatar ability and Omniknight's Repel 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.