The Nexus

Original Purpose The Antecean Nexus was the lynchpin for the Empire's longevity, success, and most importantly, reach. It connected even the most far-flung settlements and territories to each other in a way that made travelling between them as simple as traversing a city.
The theory for such a construct was originally crafted by scholars of the Logios Empire who themselves were inspired by the Former's ability to utilize the Foci seemingly as teleportation points. However, rather than use the Foci directly as the means of transportation, the Nexus tapped into their latent energy to power the scores of gates erected across the material plane. Each gate connected to a demiplane: the Nexus, also called the City of Gates.
Gates ranged from small, personal portals no bigger than a standard door to massive, city-wide structures that facilitated highway-like traffic to and from the city. The Nexus itself was constantly inundated with traffic: merchants travelling between cities, troop movements, adventurers, pilgrims, and everything in between. Mundane roads were still utilized, but usually only for short distances. The Nexus essentially served in a similar vain to airplanes today; far and away the most effective means of travel over long distances.
Structure The power siphoned from the Foci served two purposes: the first was to power the gates. This was achieved by routing the absorbed magic and dispersing it along channels like circuits and wires to individual gates which was facilitated by a central conduit inside the Nexus (Foci >> Conduit >> Gates).
The second function the Foci facilitated was the creation of the Nexus' demiplane itself. The plane was formed out of a pocket within the Astral Plane and can technically be accessed through it, though few have ever had cause to do so. Maintaining the demiplane's "structure" is done by magic again channeled through the Conduit, though this is pumped back out into the "atmosphere" and thus never goes through any of the circuitry.

Current State. The Nexus has sat in a state of degradation since the fall of Antecea over a millennia ago. The first living beings to set foot in it were adventurers allied with the White Tower Alliance seeking to utilize it to bypass the extraplanar dome that had encapsulated Eodur at the beginning of the Extinction War. Their, they found it in a state of unraveling magic that warped the very air and distorted spellcasting. What's more, they discovered the remains of humans as well as bizarre, otherworldly creatures, as well as the ghosts of souls trapped when the Nexus went down. 
One spirit in particular proved helpful in the party's endeavor and showed them where and how to reset the Conduit to allow magic to flow through it once again. After persuading a party of Gith'yanki to hold off on turning the Conduit into a bomb and aiding them in the defeat of a pair of astral dreadnoughts, the Nexus became active again for the first time in over a thousand years. It now proves as a valuable asset for the White Tower Alliance; allowing them to traverse great distances all across Archaios beyond the handful of doors equipped to Christoph Heulen's MAD (multi-dimmensional access door) system.