Modrons (pronounced: /ˈmoʊdrɑːnz/ MO-dranz) were a race of immortals known for their zealous adherence to the principles of law and order above all else. Just as fiends were considered the embodiment of evil and celestials the embodiment of good, so were modrons the embodiment of the universal principle of order.
A modrons appearance was varied and depended on their position in modron society. The most common appearance of a modron was as a geometric shape, such as a sphere or cube. The amount of sides as well as structure determined a modrons position in their society. The more sides a modron has, or the more complex their structure was, the higher they were ranked. The highest ranked modrons were humanoid in appearance. 
Modron armies battle the forces of chaos and entropy across the multiverse. Modrons use logic in developing their tactics and follow proven battle strategies. Modrons are relentless in battle, fighting without compassion or remorse, and are willing to sacrifice themselves to achieve their objective.
Regulus maintained a large fighting force composing of 36 armies. They were used for combat, defence and to maintain law and order. Each of the sixteen regions of Regulus had an army assigned to it. Three armies were used by tertians for the enforcement of law, two armies were assigned to each secundi, and the remaining nine armies were commanded by Primus, one as a personal guard and the other eight as reservists.
The structure of the modron armies, like their society, followed a strict hierarchy. Each army contained just over 400,000 modron, organized in the following structure:
|Corps||2 divisions||40 pentadrones|
|Division||4 brigades||20 pentadrones|
|Brigade||4 regiments||10 pentadrones|
|Regiment||2 battles||5 pentadrones|
|Battle||9 companies + 2 squads||4 quadrones|
All modrons were immune to mind-affecting, emotion-affecting, and magic that drew upon the Positive Energy or the Negative Energy plane. They were resistant to cold, fire, and acid. Hierarch modrons had the innate ability to duplicate the effects of clairaudience, clairvoyance, command, dimension door, teleport without error, and wall of force spells at will.
Modron culture was simple. Each modron obeyed all commands given to it by any modron one rank higher. These commands were obeyed without question. Modrons were only aware of modrons one rank higher than they were, for example, a quadrone could issue orders to tridrones, duodrones, and monodrones, but would only obey orders from pentadrones. If a modron higher in rank than a pentadrone issued an order to a quadrone, it would view it as some exceptionally powerful pentadrone. All modrons were aware of the existence of Primus, however. Modrons were unwavering in their devotion to order, departing Mechanus to complete strange tasks in the name of law. The modrons served Primus, godlike ruler of Mechanus. 
There were fourteen castes of modrons, divided in two major categories:
The lillendi, guardians of the Infinite Staircase, held a grudge against the modrons for reasons unknown. Slaads detest modrons and have waged epic battles against the forces of Mechanus for millennia.
Despite appearing as mechanical constructs, modrons are not entirely mechanical. Every modron has a mix of biological and mechanical parts, the degree of which was determined by their place in modron society. Lower ranked modrons had more mechanical components integrated within them than higher ranking modrons.
Most modrons have no sense of smell and no modron has a sense of taste. Modrons used auditory and tactile sensors. Since modrons communicated telepathically while in Mechanus, their sense of hearing was primarly used to detect sounds and to facilitate communication with non-telepathic visitors to Mechanus. Modrons felt pain and physical contact via their tactile sensors, and were able to inhibit this as required. All modrons had eyes, with hierarchs having two or more eyes allowing them to have a full field of vision.
Unlike most other creatures, modrons had no need to breathe or consume food and liquid in order to survive. Modrons required regular intake of a unique form of psychomorphic energy. It had the consistency of thick jelly and emmitted a faint inner light. It was harvested by monodrones and stored in a large pool in Regulus. Modrons had to intake this substance every few weeks or else begin to degrade.
The giant deity Annam All-Father acquired the secret of rune magic for his people from a high-ranking modron by winning a game of lots about a thousand years after the giants' war against the dragons.
Mechanus and the modrons were discovered by Netherese explorer and archmage Lady Polaris around −346 DR, who also magically bound and employed them as guards.
- ↑ Although tridrones and higher ranks could speak common in earlier editions, the 5th edition of Dungeons & Dragons removes the ability of any modron to speak in a tongue other than their native one.
- Ken Marable (April 2007). “Return of the Modrons”. In Erik Mona ed. Dragon #354 (Paizo Publishing, LLC), pp. 35–49.
- Greg Bilsland and Bruce Cordell (January 2011). “Creature Incarnations: Modrons”. In Steve Winter ed. Dungeon #186 (Wizards of the Coast), pp. 33–36.
- Brian James (August 2012). “The Ecology of the Modron”. In Steve Winter ed. Dragon #414 (Wizards of the Coast), pp. 7–15.
- ↑ 1.0 1.1 1.2 1.3 David "Zeb" Cook (1994). Planescape Campaign Setting, Monstrous Supplement. Edited by David Wise. (TSR, Inc), pp. 16–22. ISBN 978-1560768340.
- ↑ 2.0 2.1 2.2 Wizards RPG Team (2014). Monster Manual 5th edition. (Wizards of the Coast), pp. 224–226. ISBN 978-0786965614.
- ↑ 3.0 3.1 3.2 Greg Bilsland and Bruce Cordell (January 2011). “Creature Incarnations: Modrons”. In Steve Winter ed. Dungeon #186 (Wizards of the Coast), pp. 33–36.
- ↑ 4.0 4.1 4.2 Mark Jindra (2001-09-21). The Modrons (Zipped PDF). Wizards of the Coast. pp. 6–18. Archived from the original on 2016-11-01. Retrieved on 2018-09-09.
- ↑ Gary Gygax (August 1983). Monster Manual II 1st edition. (TSR, Inc). ISBN 0-88038-031-4.
- ↑ Frank Mentzer (January 1985). “Ay pronunseeAYshun gyd”. In Kim Mohan ed. Dragon #93 (TSR, Inc.), p. 28.
- ↑ 7.0 7.1 Brian James (August 2012). “The Ecology of the Modron”. In Steve Winter ed. Dragon #414 (Wizards of the Coast), p. 11.
- ↑ 8.0 8.1 Mark Jindra (2001-09-21). The Modrons (Zipped PDF). Wizards of the Coast. pp. 4–5. Archived from the original on 2016-11-01. Retrieved on 2018-09-09.
- ↑ Monte Cook, Colin McComb (1997-10-28). The Great Modron March. Edited by Michele Carter. (TSR, Inc.), p. 126. ISBN 0-7869-0648-0.
- ↑ Mark Jindra (2001-09-21). The Modrons (Zipped PDF). Wizards of the Coast. p. 2. Archived from the original on 2016-11-01. Retrieved on 2018-09-09.
- ↑ Dale Donovan (May 1998). For Duty & Deity. (Wizards of the Coast), p. 17. ISBN 0-7869-1234-0.
- ↑ 12.0 12.1 12.2 Brian James (August 2012). “The Ecology of the Modron”. In Steve Winter ed. Dragon #414 (Wizards of the Coast), pp. 9–10.
- ↑ Mark Jindra (2001-09-21). The Modrons (Zipped PDF). Wizards of the Coast. p. 3. Archived from the original on 2016-11-01. Retrieved on 2018-09-09.
- ↑ Ray Winninger (August 1995). Giantcraft. (TSR, Inc), p. 58. ISBN 0-7869-0163-2.
- ↑ slade (1996). How the Mighty Are Fallen. (TSR, Inc), pp. 3, 31. ISBN 0-7869-0537-9.
- ↑ Christopher Perkins, Adam Lee, Richard Whitters (September 1, 2015). Out of the Abyss. Edited by Jeremy Crawford. (Wizards of the Coast), pp. 179–180, 183–184. ISBN 978-0-7869-6581-6.
- ↑ Scott Haring (1988). Empires of the Sands. (TSR, Inc), p. 50. ISBN 0-8803-8539-1.
- ↑ Ed Greenwood and Jeff Grubb (September 1988). City System. (TSR, Inc.), p. 25. ISBN 0-8803-8600-2.