Mechanus

The clockwork plane, Mechanus, is an Outer Plane among the Planes of Existence representing the alignment of lawful neutral and home of the modrons.

Description
This plane is filled with an infinite number of country-sized circular interlocking gears which are habitable on one or both sides. These great flat wheels are at least 1,000 miles in diameter with teeth that meshed at right angles, all turning slowly in synchronicity. Each disk possesses its own gravity that operates in a sphere circumscribing it exactly and pulling normal to the top and bottom surfaces. The void between the gears is filled with air, allowing easy flight. Outside a gravity sphere, objects feel only very weak attraction to nearby disks.

A plane of Law and order, Mechanus has equal amounts of light and dark, heat and cold, and equal measures of the four elements. There is a place for everything and everything is in its place. Even individuals living here exist to fit into the greater scheme of things and thus achieve a perfect society. There is no pain and the only pleasure is in successfully filling a role, like a gear in a machine. Passion, fantasy, and illusion do not exist here, except for what might be brought in by visitors, and any who tried to foment individualism or stir passions for a cause encountered much resistance.

Mechanus is connected to the Prime Material Planes via the Astral Plane, and to the Outer Planes of Arcadia, Acheron, and Concordant Opposition by portals which appear once for every revolution of the gears they belong to. The period of rotation depends on the size of the gear, but a typical period is twenty days. The portals stays open for exactly one day. There is one portal to Concordant Opposition, located at the center of the featureless bottom side of a large gear, that was continually open.

Inhabitants
The only creatures native to Mechanus are the modrons, a race of beings organized in a rigid caste system and ruled by Primus, the One and the Prime. The most common modrons are the monodrones, single-function drones used as common laborers, servants, or soldiers.

History
After Orcus killed Primus and triggered an unexpected Great Modron March, he left the Energy Pool in Regulus to search for the Wand of Orcus, leaving the way open for a secundus to be promoted into the new Primus. However, prolonged contact with the Pool caused Orcus's evil influence to taint a fraction of the modrons. One tainted secundus disputed the ascension of any one of the other three and rebelled, leaving Mechanus and taking almost a million modrons with him. The dissidents settled a modron colony in Acheron, where they regrouped to later attempt to retake the plane. This schism crippled the modron race and paved the way for a formian invasion of Mechanus.

In the late 15th century DR, the wild mage, Delina, was sent to Mechanus by Martikay in order to search for a way to cure her from her wild magic surges. After interacting with several modrons, she was brought to trial by the Fraternity of Order at Regulus under charges of being an agent of chaos. She was found guilty and summarily sentenced to exile from the plane. The experience allowed Delina to better understand, rather than control, her wild magic.