On a regular schedule, the Great Modron March spills out of Mechanus and the lawful automatons files their way around the Great Ring. No one knows why they do it, but everyone stays out of their way - because when the modrons march, they'll walk right over a berk who doesn't know enough to move aside.

But this March has started decades before it was supposed to begin, and that's even more of a mystery. Caught unprepared, the planes shudder under the modrons' collective footsteps - and even the modrons themselves seem a little out of sorts.

The Great Modron March anthology features 11 adventures for characters ranging from 1st to 10th level as well as new information about the modrons of Mechanus. Each adventure can be played separely or linked together to form an extended campaign. The modron procession touches every Outer Plane in turn - and it isn't always welcome. On their unswerving path, the clockwork creatures will destroy celestial towns, be attacked by evil knights intent on using modron parts in foul experiments, and lead characters onto the deadly plains of the Abyss and into the famous prime-material labyrinth of Undermountain. Without help, they'll be lost in the swirling chaos of Limbo or even fail to complete the March entirely. And along their route, every blood on the planes seeks the answer to the most important question: Why have the Modrons abandoned their normal, lawful schedule to march years before they're due?

The Modron March is a once-in-a-lifetime event for any adventurer - and the player characters can participate every step of the way!