as found in the pages of the Zd10 Wiki
Trigates have played an incredibly important role in the history of the planes, quite frankly influencing every being in one way or another. While every world has its own unique history, cultures and ecosystems, upon becoming a planeswalking civilization they become a part of a greater whole. If it wasn't for the Trigates, the Planar Council wouldn't exist, and many worlds wouldn't be as successful as they are today. However, they also open up new possibilities of threats and disasters which certainly make them a mixed blessing.
As planar cultures developed, many societies set their eyes towards participating in the larger culture of the Planar Council, slowing down exploration on their own worlds. To those looking for adventure, a change of pace or an escape, there are plenty of opportunities on every world. To those willing to travel and put up with the rigors involved in traversing a myriad of locales, Trigates offer nearly infinite possibilities.
The Trigates are massive structures built by the Precursors that act as portals allowing for near-instantaneous transportation between different worlds. Of all the remnants found of the Precursors, the Trigates are considered to be their crowning achievement.
Trigates are incredibly large structures, taking up a quite a bit of space and generally being the tallest artificial structure on every world. Generally triangular in shape, they stand 1025ft from the base to the top, with the base having a width similar in length. They are constructed of an unknown metallic material, seemingly indestructable and unaffected by anything used on it. They are very durable, with the Trigates being incredibly ancient. The outside area of the Trigate that faces away from the portal is a bright silver color that is highly reflective. The internal area where the portal is maintained, while formed from what is beleived to be the same substance, is a darker silver color.
Inside the Trigate lies the portal, a nearly transparent white shimmering field of energy. This portal is always active, though there is no way to determine if that has always been the case.
Placing one's limbs through the portal has no effect, as the portal will only transport whole objects so that any object which has not fully entered the portal can be removed without trouble. The Trigate does not seem to send an object through until it has entirely passed through the portal, ensuring only complete objects are moved. In the event of larger objects containing smaller ones, such as vehicles used for transporting goods or people, the larger object itself counts as a single object of higher priority than its contents. Depending on which side of the portal is entered determines the exiting side on the other end. As both sides of the portal are usable, it can appear that two objects are "entering" each other, while they are in fact entering the portal at the same time.
The portals are capable of conserving momentum, so caution should be used when entering it to prevent accidents. An object sent through at a certain speed, such a person running will maintain the same speed when exiting on the other side. Due to this, it is also possible to fire physical projectiles through the portal and harm others on the opposing end. Projectiles that are more energetic in nature are seemingly just absorbed by the Trigate. The portal is able to determine the difference between passive and active contact of nearby matter in order to prevent unwanted transportation. This process keeps things such as air and water, which naturally exert pressure on their surroundings, from passing through the Trigate while allowing people and anything deliberately sent through the gate to pass freely.
Though the civilizations lack any real way to ultimately determine the exact age of the Trigates, they are undoubtedly the oldest things on many worlds, along with other Precursor ruins. It should be said that other ruins are exceptionally rare however, so the Trigates are the main and primary source of information regarding the Precursors.
An interesting note that raises questions in many scholars is the fact that the worlds the Trigates have been built on change with time, but the Trigates still remain upright, fully functional and on the surface of these planes. There are many theories on this, but nothing has been conclusively proven.