Tempus refers both to the world of Tempus and its main continent.
The written history of Tempus stretches to 6,500 BU, when the elves were brought into the world.
Tempus consists of five planar circles.
The center circle is the Prime Material Plane, also simply Tempus. It is the plane of most everyday interactions, and it is the most populated plane. It is also the plane with the largest area.
The second circle is the Inner Planes, or the Elemental Planes. They are the planes of Water, Earth, Fire, and Air. They provide elemental material for the construction and sustenance of the Prime Material Plane.
The third circle is the Outer Planes, or the Aligned Planes. They are planes with moral alignments, and they affect the souls and drives of people across the circles of Tempus.
The fourth circle is the Outlands. It is a relatively small, approximately circular plane that allows for travel across the circles of Tempus. The portal city of Nexus is here, as well as the magical site Fargate.
The fifth circle is the Farplane. It is an infinitely large plane that has been largely unexplored. It is only accessible via the Fargate.
Current deciphering of the Fargate suggests that Althyk originally created the Outlands. The other planar circles were later created, for unknown purposes.
In 6500 Before Unification, or BU, Elves were introduced to the Prime Material Plane. They brought hunting, writing, and magic with them. Dwarves came in 5000 BU, bringing mining, smithing, and the wheel. Humans, halflings, and gnomes entered in 3000 BU, along with farming.
In 900 BU, inspired by Ifrit, the five races signed the Sky Treaty with the dragons. This treaty was annulled in 300 BU, starting the War of the Heavens. Breaking the treaty introduced the dragonborn to Tempus. As of 1601 AU, this war has not ended.
The current year is 1601. As of today, Unification is still the most historically significant event that has occurred, allowing the 11 countries of the world to easily meet with each other.