In Mertion, the Platinum Heaven, is Rempha, the City of the Sands of Time (Planes of Law: Mount Celestia, p. 23). It was created by a rogue modron named Secondus to house and care for a massive portal to the temporal plane. Secondus’ history on its plane of origin (or even if it was in fact a member of the secundus caste) is mostly unknown, but it’s assumed that it became increasingly obsessed with the chaos it preceived in Time and destiny, and increasingly concerned that its superior didn’t do something about it. Eventually this concern blossomed into individuality, and Secondus left the Clockwork Universe forever in a quest to discover how to monitor and manipulate Time itself.
Exploring the Deep Ethereal, Secondus eventually found evidence of the Temporal Energy Plane in the form of the chronolilies that grow there. Building a spherical research base on the edge of the shimmering curtain that led to the plane, Secondus spent centuries experimenting with raw temporal energy. It fashioned mechanical constructs (mentioned in the Manual of the Planes, 2001 edition, page 209) and sent them into the timewinds to record and bring back information; most never returned, and many still drift through the plane to this day, having gone as rogue as their creator.
Some returned, though, and with the aid of the Prime wizard Aionias (the so-called Saphire Mage; A Guide to the Ethereal Plane, page 79) the modron began to make progress. Using the skills they had developed, Secondus and Aionias peered back through the mists of time… and saw infinite horror.
Aionias’ mind shattered, and Secondus had to put him down in order to preserve itself. Afterwards, Secondus surmised that the temporal plane, and possibly Time itself, had been deliberately created by some ancient intelligence to shield the rest of the multiverse from the alien strength outside it. The modron’s goals changed; Secondus no longer saw Time as a chaotic force, but as an agent that protected the multiverse from outer Chaos. Rather than being determined to manipulate the timewinds, Secondus became convinced that its true purpose was to protect them.
After continuing in less invasive researches for another seven decades, Secondus left the Waveless Sea to seek the patronage of a race it believed would help it in its goals. As a rogue, it could never return to Mechanus, but there existed another people of incarnate Law that had an interest in protecting the cosmic order.
Of course, it went to the baatezu. The lords of Baator seemed interested in Secondus’ discoveries, particularly the servants of the pit fiend Pearza. They even built a prototype of a time skiff before it dawned on the modron that the baatezu were more interested in manipulating Time than preserving it. While the cornugon supervisor was in a dormant cycle, Secondus destroyed the machine and used a special pod it had added to escape, and try again.
The archons in Heart’s Faith were skeptical, but they allowed Secondus an audience with the Warden Gamirion when they found out it had been working with the baatezu.
Secondus showed the warden a device it had salvaged. Gamirion was impressed. News of the visitor and its inventions traveled quickly through the hierarchy, and before long the founding stones of the City of the Sands of Time were being laid.
Today Rempha is in constant operation. Timewinds blow out of the portal in the city’s center at all hours, causing the seasons and cycles of light around the burg to change erratically.
In the rings of buildings outside the gate on the side of the Holy Mountain, archons and petitioners craft mundane timekeeping devices, magical hourglasses the Grim Reaper wouldn’t be ashamed to own, and other goods of an unusually durable nature. Here, too, are the archons of time: the angels of the constellations, of the days of the week, of life and death and night and day. These celestials act as spiritual guides to mortals during their designated periods of influence. Pilgrims from the Dustmen sometimes stop here to pay tribute to Azrael, the celestial aspect of Death.
A golden-pillared embassy hosts temporal dimensionals (see Chronomancer, or the Monstrous Compendium Annual, volume 3) and other beings found or rescued from the temporal plane.
Rempha is actually constructed in two distinct parts, with half actually located in a hidden glacial valley on the material plane. The material half of Rempha has a portal on each end, one leading to Celestia and one leading to an ethereal plane. It is here that the celestial time police, mostly specially adapted monadic devas, train in secret, with even the archons of Rempha ignorant of their true mission due to the sensitivity of the plots they’re trying to unravel. In Rempha’s years of activity, the celestials have discovered that they aren’t the only ones researching the effects of the temporal plane. Several ancient civilizations had done the same in the past, only to be destroyed or caught in endless time loops – a fate they wish to prevent from happening again. There’s a fear that the Bringing, a pet project of the baatezu the celestials are keeping close tabs on, might involve chronomancy. In addition, there’s evidence of illithids making tentative ventures into the plane, perhaps trying to resurrect their ancient empire. Finally, a great deal of temporal anomalies have been detected in the ethereal mazes created by the Lady of Pain; agents have been sent to explore some of those, but very carefully indeed. Some are snooping around Sigil instead, investigating the Hall of Records and the home of a bladeling wizard in particular.
Secondus has not been idle. Besides avoiding assassination attempts by both the baatezu and the modrons, it has been working on designing what it believes is the ultimate portal to the temporal plane. The size of a city, the device will supposedly allow those who pass through it to travel against the timewinds as easily as with them, and thus avoid the unpredictable effects chronovoyagers must normally face. Time will tell.