Stone Monoliths carved to allow people to pass through the center and be instantaneously transported to the connected Monolith regardless of distance.
The technology isn't largely understood, almost seeming magical, however, advanced math classes cover the formulas required for calibrating them and advanced science details the chemical makeup needed for the stone to be artificially created. Different branches of specialties come together to create the phenomenon known as Portal Travel.
There's a white flickering light emitted from the center of a fully intact portal, indicating it's safe to use for travel.
Side Effects
As with most technological advancements, some adverse effects are noted among a number of the populace. While most will be able to use Portal Travel without any noticeable side effects, some may experience nausea, dizziness, seizures, and/or intense psychological distress.
Note: Some of these symptoms may be treated with a modification to the implant to dampen the users senses within a certain proximity to a working portal.
History
While the first working portal has been lost to history and debated by many elite historians, we do know that Portal Travel became a government run mode of transportation in 1309 when Archon Xaiden Caelus XXXVII (Also known as Xaiden the First) became Archon and spearheaded the process of implementing them throughout Zenith.