What’s a mortal to make of the modrons—those strange creatures of absolute order that whir and click along in the Clockwork Nirvana of Mechanus? To an outsider, they seem to have no existence other than as a whole. Indeed, there is a saying: “To look at one modron is to look at all of them.” It is only logical that these creatures are native to Mechanus. Rumor has it that they are the keepers of their mechanical plane, the maintainers of the gears and the polishers of the cogs. Modrons keep the whole place running smoothly and cleanly—without them, Mechanus would surely break down. Though the majority of modrons live in Regulus (their own city in Mechanus), they can be encountered anywhere within the planes. No modron is ever without a task to carry out, though these tasks may be no more comprehensible to other creatures than the modrons themselves are. Just what are the goals of these creatures of ultimate order? Do they want to impose total law over the rest of the cosmos? Are they simply keepers of the machinery that drives the multiverse—the repair unit of infinity? Or are they devious players on the cosmic gameboard, trying to eliminate their competition? These questions may never be answered, and a host more may never be asked. No one but a modron truly understands a modron.


The city of Regulus occupies sixty-four of the coglike wheels of Mechanus, called sectors. Each group of four sectors is called a region, and each group of four regions is called a quarter. Modrons of increasingly greater authority oversee each of these units, and over it all reigns Primus, the One and the Prime, supreme ruler of all modrons. The Tower of Primus stands at the hub of the central cog and the modron cathedral (see below) rises from one close by.



No. of Members

Body Shape


Telepathy Range (Miles)

The One and the Prime

Absolute ruler of all modrons
All Mechanus

Hierarch Modrons

Viceroys of the quarters
3-armed humanoid
4-armed humanoid
Rulers of the regions
5-armed humanoid
Bureau chiefs and recordkeepers
6-armed humanoid
Generals of the modron armies
7-armed humanoid
8-armed torpedolike creature
Governors of the sectors
9-armed cylinder
Police supervisors
10-armed sphere
Supervisors and caretakers of base modrons

Base Modrons

Law enforcers
1.5 million+
Multifunctional laborers, supervisors
6 million+
Trifunctional laborers, minor supervisors
55 million+
Bifunctional laborers
300 million+
Single-functional general laborers


In all, there are more than 360 million modrons, divided into fifteen ranks, or castes. Castes are hardly unique, but the modron approach to them is. Each caste has not only its own functions, but its own body shape as well. Thus, a modron’s physical appearance is a direct indicator of its rank. The castes are further categorized into base modrons and hierarch modrons. Base modrons perform mundane tasks; hierarch modrons plan and organize, oversee others, and manage entire areas. At the top of the list, of course, is Primus. From greatest to least, the fifteen modron castes are listed on the table below. Listed with each is the number of modrons in that caste and a brief description of their duties in Regulus. Primus and the hierarch modrons are also capable of telepathic communication, and the range of that power is given in a separate column.


Though the number of modrons in each caste is fixed, the DM may decide the actual figure for each of the base modron castes. No individuality, in either form or thought, exists within a caste. Each modron calls itself “we” and can interchange posts and positions with others of the same caste. Thus, a traveler has no way of knowing whether the pentadrone encountered today is the same one who held that post yesterday. This would be only a minor inconvenience were it not for the rigid and complex bureaucracy of Regulus, which requires visitors to appear and reappear before clerks, courts, and boards before even the smallest of requests can be granted. Occasionally a clever character solves this problem with a brush and paint, marking individual modrons with runes to tell them apart. Unless instructed to remove such marks, a base modron may wear a splash of color or a strange sigil for the rest of its life, for most do not even notice such things as markings on their own bodies. This rigid caste system also defines the modrons’ ability to interact with other members of their own race. Each modron is aware of and recognizes other modrons of the same or lower caste, as well as those of the nexthigher caste (their supervisors). Modrons more than one rank higher simply appear as incomprehensible creatures. Of course, a pentadrone might be assigned to guard a hexton, but it understands only that it is to guard a creature matching the description of the hexton; it has no conception of that hierarch’s place in the overall social structure. Likewise, a duodrone assigned to maintain the residence of a secundus does not understand who built that structure or why.


Some speculate that the modrons descended from some type of intelligent insect, and that this heritage has given them an incredible hive mind. There is, of course, no proof of this theory, nor is there really any way to check. Whatever their ancestors may have been, it’s clear that the modrons function in a communal manner, right down to life and death. Long ago, the modrons somehow learned to place energy into a central pool in Regulus and draw it back out again to power their own forms. When a modron dies, its life force is absorbed back into that pool, and a modron from the next lower rank is immediately promoted to replace it. This in turn creates a gap in the caste below, which is filled by promotion from the one below that. This process continues right down to the monodrone level. Monodrones, having no castes below them, reproduce by fission to replace lost members. The new monodrone formed when an existing one divides draws its life essence out of the pool. (In light of this life cycle, the claim that all modrons are one might be truer than it first seems.) Individual promotions occur seemingly by accident. Since modrons have no individuality, there’s no point in trying to promote the “best and the brightest”—all modrons of a given rank are equal. Thus, the nearest one of an appropriate rank is promoted when a vacancy occurs. This process of promotion is traumatic—not only does the chosen modron undergo a wrenching change of shape to the new rank’s form, but it suddenly gains knowledge previously veiled to it—the existence of another superior rank. Imagine the shock of a duodrone, which previously knew only of monodrones, duodrones, and tridrones, when it undergoes a promotion to tridrone. Suddenly, it discovers that some of those inexplicable creatures around it are quadrones— members of its own race and its new superiors! Nevertheless, a newly promoted modron seems to adapt instantly to its new form. Indeed, it is the humanoid observer who is often most shaken by the experience.


Because of their method of reproduction, modrons have no families, tribes, or clans. They live in rigid numerical units called, for lack of a better word, battalions. This term makes modrons sound more warlike than they really are, although they do maintain standing armies that are not to be trifled with (see The Armies of the Modrons, below). Modrons spend their lives performing the duties that Primus assigns, either directly or indirectly. Each modron accepts orders from members of the nexthigher caste and can, in turn, give instructions to members of the next-lower caste. In this way, orders filter down from Primus through all the modron ranks until they reach the caste capable of carrying them out. Although some less-informed scholars state that no modron acts except by the orders of a superior, this is not perfectly accurate. In general, a modron can act and react on its own, provided that the situation at hand falls within the range of its purpose. Thus, monodrones are rightly seen as incapable of reacting because each can perform only a single task at any given time. Modrons of higher ranks have correspondingly greater ranges of function, so they can react to more and more complex situations. Even so, modrons are notorious for their predictable and rigid reactions to events.


Modrons are the ultimate creatures of law. Their very bodies conform to the unflinching regularity of geometry, and the flawless logic of their alien minds can lead them to conclusions that others might not even consider. Modrons have pitted themselves against—and beaten—all challengers at games of logic, so their supremacy in that area is undisputed. Modrons care only about order and law; they have no concept of good and evil. They can decide what is best and what is worst, but they cannot distinguish between right and wrong. This limited viewpoint makes dealing with these creatures a challenge. Attempts to explain good and evil to a modron can only result in it equating good with order and evil with chaos, for those are the best and worst possibilities it can imagine. It should be no surprise that the goal of every modron is to organize Mechanus in the most orderly fashion possible. Given the opportunity, of course, modrons would spread their rigid pattern of organization over the entire multiverse. Fortunately for the rest of the planes, order is constantly challenged by chaos, even in the clockwork vastness of Mechanus. Since even the slightest imperfection is enough to disturb the ultimate harmony that modrons seek, they seldom find the time or resources to carry their crusade to other realms or planes.


Modrons are not completely without their uses to the residents of other planes. In fact, their single-minded pursuit of order is particularly beneficial in some areas. Wizards, for example, find that modrons make amazingly effective librarians, and some merchants appreciate having them as bookkeepers. On rare occasions, nonmodrons can hire modrons for particular tasks. The process is never simple, since the potential employee can never make that decision itself—all requests are subject to approval by superiors. Usually the request has to pass through several castes before an answer is forthcoming. Those who employ modrons must be constantly on guard against the creatures’ overzealousness. Sometimes a modron’s understanding of order, which is far deeper than that of most other beings, defies human comprehension. For example, a modron might decide to arrange all the books in one library by subject, in another by the first letter of the first word, and in yet a third by the page where the last diagram appears. All three of these approaches might somehow be vital to maintaining the overall order, as defined by the modrons. Order, after all, does not necessarily need to be understandable. Modrons’ attitudes toward their employers and coworkers can vary for no apparent reason. Sometimes these creatures are helpful, and sometimes they’re cruel—but they’re never entirely predictable in their dealings with other races. No one except other modrons can read a modron’s expression or guess at its true agenda. Thus, nobody with any sense really trusts one, even if it has been instructed to help. After all, it might have additional or competing orders from above, and it’s certainly not going to think twice about obeying those.


Of course, every rule has its exception, and rogue modrons are the exceptions to the rule of orderly modron society. Rogues are modrons who, for one reason or another, suddenly find that they cannot accept the orders of their superiors, or that they have lost the concept of the orderly modron society. Modrons who spend long periods alone, or have many superiors, or who advance in Hit Dice (thus becoming different than others of their rank) are the ones most likely to “go rogue.” Naturally, the modrons have tried to cut down on the factors that lead to this outcome, but there’s an indefinable factor in operation that they can’t isolate or identify. The most dangerous aspect of rogue modrons is the fact that they retain the power of command over lesser modrons. Though most rogues simply go off alone to explore the individuality they’ve discovered, it’s not unheard of for one to gather lesser modrons about it and establish its own power base. This makeshift army then goes forth to conquer, though for what purpose only the rogue itself could explain. Because of the possibility that such a creature could subvert others and wreak havoc on the order of Regulus (and even Mechanus as a whole), rogues are considered menaces to modron society. The hierarchs pour almost every resource they have into hunting them down, bringing them to trial, and destroying them. This is a difficult process because it’s often hard to tell when a modron goes rogue. A modron who told others of lower ranks to disobey their superiors would surely earn the designation of rogue, for this is tantamount to blasphemy in Regulus. But it is rare for even rogue modrons to do this because of their innate respect for order.


The modrons maintain thirty-six great armies, each a powerful fighting force in its own right. One is stationed in each of the sixteen regions of Regulus, and each secundus maintains two armies in addition to its regional forces. Three armies are assigned to the tertians, to aid them with law enforcement and punishment. The remaining nine armies serve Primus directly. One of these acts as the official tower guard; the other eight are available as a reserve force for dispatch as needed. Each army is commanded by a hexton and comprises four corps, each commanded by forty pentadrones in constant telepathic contact with the hexton general. Every corps has two divisions (each led by twenty pentadrones), every division has four brigades (each led by ten pentadrones), and every brigade has four regiments (each led by five pentadrones). The regiment is the standard tactical unit of the modron army. It consists of two battles (each led by four quadrones), plus a squad of winged monodrone messengers and a special squad of twelve pentadrones. A battle comprises six regular companies of monodrones, two regular companies of duodrones, a special company of tridrones, a squad of quadrones, and another squad of messengers. A company consists of twelve squads (each with twelve troops and a noncommissioned officer called an NCO) and three officers. Each of the eight regular companies in a regiment is further divided into two wings plus a headquarters unit. Special units of messengers, shock troops, and the like may also be attached to a company’s headquarters. In all, a standard regiment consists of 70 officers, 192 NCOs, 252 messengers, and 2,628 line troops, for a total of 3,142 modrons. Despite the regimented order of their armies, modrons do not fare as well in war as other planar beings. When it comes to combat and the sheer cruelty that often accompanies warfare, modrons usually come out the losers.


Once every Grand Cycle (seventeen cycles, each of which is about seventeen years—the time it takes for the largest gear on Mechanus to turn once), a horde of modrons spills out of Mechanus and marches through the planes. Why? Nobody knows for sure, although it seems as if they’re gathering information as they march. The modrons cause all kinds of havoc in the planes through which they march. They don’t stop for anyone or anything, trampling right through towns and over any inhabitants who are too slow to get out of the way. It is ironic that these lawful automatons can be the cause of so much chaos. When they reach the Lower Planes, the conflict begins in earnest, with the inhabitants attacking the invaders from Regulus every step of the way. When the much-reduced force returns to Mechanus, the few remaining troops march straight to their superiors to report. What they say in this meeting is the subject of much speculation: Some claim that they report on the progress of the modron invasion; others insist that they merely describe the state of the planes. Granted, this seems a difficult way to gather knowledge, but perhaps the modron mind sees some particular logic about it. Whatever the case, the report is inexplicable to everyone except modrons. Over the centuries, the inhabitants of the other planes have grown accustomed to the March. Previous Marches are well documented, and an adventurous few have roughed out some of the probable routes for upcoming ones.


The modrons share Regulus with two other unusual creatures: the moignos and the coggles. These creatures have their own functions within the rigid structure of modron society.


Next to modrons, the most common creatures in Regulus are moignos, two-dimensional mathematical constructs that act as calculators for modrons. The tiny, strange moignos are devoted to finding the exact value of pi, which is widely acknowledged as an endless task. During pauses in this endeavor, they also perform a variety of calculations regarding gear movements and pass this information on to the modrons.


Coggles resemble the great, coglike gears of Mechanus. They move about the plane at will, adding themselves to the workings of Mechanus here and there for short periods, then moving on. Coggles range in size from only a few hundred feet to almost a mile across. A large one can serve as a transport for an entire battalion of modrons. They may serve other purposes as well, though these are beyond the comprehension of those not native to Mechanus. Coggles can speak and understand the modron tongue.


Deep in the heart of Regulus, there stands a tower that appears to defy all the laws of mechanics. This modron cathedral, as it’s called, reaches far, far into the sky and seems much too slender for its height. Inside, it’s a vast place—much wider, taller, and deeper than its outer dimensions should allow, with a vaulted ceiling that disappears into darkness. Within this tower is a device that the modrons have been working on for years, and it is said that to look upon their creation is to go mad. According to rumor, Primus uses this item to keep track of the goings-on across the infinite planes. The modron cathedral rises out of the central gear of Regulus, not far from Primus’s tower. Surrounded by lesser buildings, it resembles nothing so much as a huge church steeple rising high into the sky. The modron cathedral isn’t nearly as tall as the tales claim, nor is it really bigger on the inside than its outer dimensions would allow. It does seem that way because of some tricks the modrons have played with perspective, but if someone were to measure the entire structure with painstaking accuracy, it would measure up just right. Modrons are constantly buzzing across the cathedral, keeping it polished, adding fixtures, taking others away, and guarding against intruders. Each visitor wishing to enter must have a pass specifically for the modron cathedral from the Central Office of Processing and Requests, and even then an escort consisting of at least two pentadrones per person must accompany any such group. The interior of the cathedral is absolutely huge. The stone walls support vaulted ceilings that seem to spring into the sky, their upper reaches lost in shadows. Balconies on hundreds of floors ring the open space in the center of the structure, and modrons of various ranks constantly move along the balconies on errands. The central feature of the cathedral’s interior is the Orrery, a gigantic device built of constantly moving gears. Spheres inscribed with various symbols rotate about the device’s central point—a needle that rises into the steeple of the cathedral. A successful Knowledge (planes) check (DC 15) reveals that the inscriptions on the spheres are in fact the symbols of the planes. Anyone who watches the Orrery tick and whir for at least 1 hour can attempt a Knowledge (planes) check (DC 30) to discover that the device is actually a working model of the planes, incredibly detailed and infinitely complex. By concentrating on a particular feature of the Orrery as it moves, a viewer can use it as a giant scrying device to view what transpires on the plane corresponding to the chosen point. Failure by more than 5 on any check made either to use or to understand the Orrery results in confusion, as the spell cast by a 20thlevel sorcerer, but affecting only the individual who failed the check. The Orrery also has the power of teleportation, though no one except Primus and the secundi knows how to initiate that function. These hierarchs find the device quite useful for planar transport. The modrons, of course, do not allow visitors the time to examine the device, and doing so by stealth is difficult, as neither the Orrery nor visitors are ever unattended. There are always at least a few modrons perched on the device, swabbing at one surface or another or making precise adjustments. Anyone caught using the Orrery without permission is killed, no questions asked. Few other than modrons even try to use the device anymore because of its reputation for causing insanity.


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