Barrier, a perfect defence shield preventing all matter and energy, even TARDISes, from passing through without authorisation. The Time Lords are further protected by phasing the entire region around Gallifrey into a temporal domain known as Inner Time, effectively separating the homeworld from interaction with the rest of the Universe. During the final hours of the Time War, the High Council of Gallifrey refer to defenses called 'Sky Trenches' which appear to be at least somewhat effective against invading Daleks and/or their ships, as seen in "The Day of the Doctor". TARDISes are characterised not just by their ability to travel in time, but also their dimensionally transcendent nature. A TARDIS' interior spaces exist in a different dimension from its exterior, allowing it to appear to be bigger on the inside. The Doctor states that transdimensional engineering was a key Time Lord discovery in The Robots of Death. In the Ninth and Tenth Doctors' episodes, the TARDIS has an organic look, and the Doctor states in "The Impossible Planet" that TARDISes are grown, not made. It is seen in "The Name of the Doctor" that as a TARDIS dies, its 'dimension dams' can break down causing a 'size leak' wherein the exterior dimensions of a TARDIS begin to expand to match its inner dimensions. Fitting their generally defensive nature, Time Lord weapons technology is rarely seen, other than the staser hand weapons used by the Guard within the Capitol. Standard TARDISes do not generally seem to use any on-board weaponry, although War or Battle TARDISes (armed with "time torpedoes" that freeze their target in time) have appeared in the spin-off media. In the novels, the Eighth Doctor's companion Compassion, a living TARDIS, has enough firepower to annihilate other TARDISes. In the serial Castrovalva, the Master's TARDIS is equipped with an energy field that he uses to temporarily disable or stun several human security guards outside the vessel. One exception to the Time Lords' defensive weaponry is the de-mat gun (or dematerialisation gun). The de-mat gun is a weapon of mass destruction that removes its target from space-time altogether, as seen in The Invasion of Time. The de-mat gun was created in Rassilon's time and is a closely guarded secret; the knowledge to create one is kept in the Matrix and is available only to the President. To make sure this knowledge is not abused, the only way to arm a