There's a ton of misconceptions about the Tribunals power in The Elder Scrolls. I'll make it clear now; they aren't just powerful warriors or wizards who can destroy countries, they're bonafide gods who can create and destroy entire universes, possibly everything. Let's begin with Sotha Sil. Sotha Sil is the Clockwork God, who created the Clockwork City.
ESO Live - Clockwork City First Look said:
Jessica Folsom: So you can't actually...walk to Clockwork, right?

Leamon Tuttle:
No. Clockwork City exists outside of space & time. ...It gets weird man! It gets way weirder that that!

This is basically...the Clockwork City is...for what people think it's a city in miniature inside of this snow globe deep under Mournhold.

Jessica: So is that actually Clockwork City are you getting shrunk down like Honey I Shrunk the Kids?

Leamon Tuttle: Yes, that is a super good question. It is and is not the Clockwork City. It's a representation and also like I said the Clockwork City exists in a kind of an interdimensional space.

So it's there and it's also not there, it's a lotta crazy questions...that don't frankly have very many answers in the Clockwork City.
The Clockwork City exists outside space and time within interdimensional space.
ESO Live - Clockwork City First Look said:
Leamon Tuttle: This was the Demonic Planisphere, it's another one of Sotha Sil's kind of ongoing projects. This one actually he has not abandoned; you learn over the course of the quest that the planisphere has a very direct relationship to Sotha Sils memory. He uses this as a big kinda storage facility for all his various memories that he's offloaded for one reason or another, so...each of these little stars as you learn over the course of the quest relates to a memory of the Clockwork guy.

Jessica Folsom: That's awesome, wow.

Jeremy Sera: ...It does not look this finished...until you have completed the quest.I didn't want to show you the unfinished version which doesn't look quite as awesome.

Leamon Tuttle: You'd be surprised to hear that something bad has happened here!
The stars in the Clockwork City aren't rips the Aetherius, but are actually his memories.
ESO Live - Clockwork City First Look said:
Jeremy Sera:...As you're wandering around the stars actually have little titbits of (???) memory that you'll hear. You'll hear Sotha Sils memories some that are very specific to the quest content and others that are random things that he may have ever heard.

Leamon Tuttle: Even though you don't see Sotha Sil very often, Sotha Sil is...present in just about everything that you do in the Clockwork City. The Clockwork City in many respects kind of is Sotha Sil. So you can expect to learn a lot about him and what makes him tick!
The Cockwork City is an extension of Sotha Sil.
ESO Live - Lore of Clockwork City said:
Lawrence Schick: So the Clockwork City is the Clockwork God Sotha Sils experimental miniature recapitulation of the entire Mundus, in one small, apparently small, container. And it's built in order to both imitate and recapitulate the world above. And it's somewhere beneath Tamriel... The way you get to it in the game is through an entrance near Mournhold in Morrowind but where it is actually is it's as deep as is possible to be, and still be in Tamriel, so it's the same distance from everywhere. And it's both tiny and at the same time a world unto itself. And it's both tiny and at the same time a world unto itself. So once you get into it, it feels vast, and it is vast and at the same time it's tiny. So both of these things are true and they're not contradictory. And inside you will find that Sotha Sil has built mechanical replicas of various aspects of the world above which are being used in experiments by his clockwork apostles to test out his various theories on how the world, which was created originally of course by the Aedra, when they sacrificed themselves to become the Earthbones. When they created the world, it was in the opinion of Sotha Sil, a flawed creation and he is looking for ways, where thereby it can be perfected.
Sotha Sil's Clockwork City is a replica of the entire Mundus, where Sotha Sil where he runs experiments to see how he can perfect the world, and reshapes the world from his hidden city.
ESO Live - Lore of Clockwork City said:
Lawrence Schick: There have been various statements in lore about where it is located, but really that's about ways to get to it rather than where it can be found. Where it is is a more metaphorical location than physical really, because it's a metaphor made maniphest. It's both a reality and replication of reality at the same time.
The Clockwork City is a Manifest Metaphor.
ESO Live - Lore of Clockwork City said:
Gina Bruno: You say most of the people in Clockwork City seem to be at least above magical and/or tech ability, and everyone seems to hate the nutrience paste for being boring. Illusion magic exists, so if there's a spell to make someone think you a frind, why isn't there a spell to...make someone thing the paste tastes like scrib jelly?

Lawrence Schick: You wanna take this one?

Leamon Tuttle: Sure. First to start off, the clockwork apostles will probably tell you that Illusion Magic is profane, and they don't want it in the City. Sotha Sil is interested in truth...and yeah, finding the absolute facts of things. So creating an illusion is a ridiculous thing to even consider. Also, there's the very real possibility that Sotha Sil makes it so they have to taste it that way. The Clockwork City in many respects kinda is Sotha Sil, and there's no guarantee that any magic that an apostle or anyone else may be able to use could change the taste of the paste if he doesn't want them to.
Sotha Sil decides what kind of magics do and don't work in his domain.
ESO Live - Lore of Clockwork City said:
Gina Bruno: What kind of metal does Sotha Sil use?

Lawrence Schick: He uses every kind of metal, and some that are unknown to magic or science elsewhere. He is a master of all materials.
Sotha Sil is a master of all materials, including unknown ones.
ESO Live - Lore of Clockwork City said:
Leamon Tuttle: Everything that happens in the Clockwork City is a direct manifestation of what he wills. So it follows that probably he wants those factotums to play really bad music.
Everything that happens in the Clockwork City is a direct manifestation of Sotha Sil's will.
ESO Live - Lore of Clockwork City said:
Gina Bruno: Somebody was asking if...if the Clockwork City is some sort of parallel universe and if it's endless.

Lawrence Schick: Kind of. Both those questions is kind of. In fact it's a deliberate parallel universe, in that it deliberately parallels Tamriel above. And...what was the second part?

Gina Bruno & Leamon Tuttle: Is it endless?

Lawrence Schick: Is it endless? You don't see nearly all of it from what you can see of it in the game. It has layers, and only Sotha Sil knows the full extent of those layers and what the functions of some of the other areas are...Samantha, could you please just lean back and look up at the sky for a moment there? Look up there, look at those whirling rings spinning around the world of the Clockwork City. That is the outside of the Clockwork City...or maybe not. That's just what you can see from the Brass Fortress, and you can see that Sotha Sil has taken the concept of wheels within wheels and worlds within worlds and has made it manifest right over your head. So you're constantly contemplating the fact that the world is a built thing and therefore it can be reverse engineered, reengineered and improved! Look, there's the proof right above your head! So yeah, it's profound as hell! Goddamn this stuff is deep!
The Clockwork City is a reality of infinite size, with the Radius only being the innermost layer. There are Wheels within Wheels and Worlds within Worlds. Note that Wheel can also mean Aurbis.

The stars in the Clockwork City are made of star-data composed of Seht's memories.
Loading Screen (Clockwork City) said:
"Ordinary people keep a journal. Sotha Sil decided to store his memories as star-data in an artificial astronomical matrix keyed to his philosophical musings on the structure of the Aurbis. Of course." -Almelexia
The Clockwork City replicates the mythic structures of the world.
Loading Screen (Clockwork City) said:
The Clockwork City, also known as Sotha Sil, after its creator. is said to be a great and intricate mechanism that duplicates the mythic structures of Nirn in metallic miniature. Only Seht himself knows its true purpose.
The Clockwork City can scan the Mundus and create a clockwork duplicate form of anything, alive or not.
Loading Screen (Morrowind Online) said:
It is said that Sotha Sil's Fabrication Chambers can analyze anything in the Mundus, organic or inorganic, and reproduce it in clockwork form.

The Clockwork City has the power to not only reshape the entire material plane, but remake or even destroy it.
Elder Scrolls Online said:
Lilatha: Yes, of course. I sometimes forget that this is not common knowledge. Sotha Sil, brother to Vivec and magus of the Tribunal, created the Clockwork City long ago. He rarely speaks of it, but scholars believe this city has the power to remake Tamriel.
Vestige: Remake Tamriel? What do you mean?
Lilatha: The city functions as a simulacrum of the corporeal plane. Making a change to the Clockwork City may well change some aspect of Tamriel itself. This is all speculative, but I've studied under Sotha Sil. I have no doubt that this is within his power.
Vestige: So if someone took over Clockwork City, they could change or even destroy Tamriel?
Lilatha: Indeed. An unwelcome prospect, to be sure. Normally I would assure you that Sotha Sil has the situation well in hand. He is a friend to the Psijics, and to the people of Tamriel. But the presence of this Daedric artifact gives me pause.
Clockwork City said:
Divayth Fyr: Sotha Sil hides everything. But more to your point, it's not just a city. It's an incomprehensibly powerful world-shaping device. Can't leave that sort of thing lying about, can you?

Also, Almalexia worries about how it reflects on her divinity.
After Nocturnals true "form" breaks through the defences, she engulfs the entire Clockwork City in seconds. Divayth Fyr holds her back long enough for Sotha Sil to be reunited with his shadow. Upon gaining his full power back, he banishes Nocturnal from the Clockwork City.
In-game command (Legends) said:
Use the Heart - Battle of the Gods: You have infinite magicka and your hand refills every turn.
The Mechanical Heart of Lorkhan (which is a copy of the real Heart of Lorkhan) created by Sotha Sil embues it's users with an infinite amount of magicka. It was made to power the Clockwork City City after Almalexia killed Sotha Sil, as he was doing that before.
Return to Clockwork City said:
Kellen: Mecinar was defeated. But the hero paid a heavy price. The energy of the heart proved to much to hold within their physical form.

The hero's body disintergrated.

But the Clockwork City lived on, powered by the heart, and Galyn believed that the hero's conciousness lived on there, a whisper in the still-churning machinery.
Should the Hero choose to use the Mechanical Heart, the sheer power destroys their body. Note that Sotha Sil and the rest of the Tribunal (as well as Dagoth Ur and the Sixth House) can use the Heart of Lorkhan indefinately.
Morrowind Online said:
Vestige: He went to a lot of trouble just to steal your divine energy.

Vivec: Every move...has a purpose. Stealing my energy sowed discord and disaster...throughout the land...and ultimately revealed the location of...the Clockwork City. If Barbas and his master can bypass the wards and enter Sotha Sil's domain...

Vestige: This has all been a ploy to find the Clockwork City?

Vivec: Clavicus Vile distracted me, weakened me...all to locate the Clockwork City. Perhaps we require a Daedra, to fight a Daedra. Azura's champion, Archcanon's office. Seek guidance from her patron. But, hurry, my time grows short...
The Clockwork City's power is so great that even the Daedric Princes seek it (and it has it's own wards to keep the Daedric Princes out).
Morrowind Online said:
Azura: So Vivec deigns to ask for help? I foresaw such an event, but scarcely believed it.

Listen well, for if you continue to perform flawlessly, we might yet thwart the efforts of Clavicus Vile and his hound, Barbas.

Vestige: Lord Vivec said to ask you for guidance in this matter.

Azura: Just as I anticipated. The mysteries reveal that Barbas seeks to enter the Clockwork City. So far, Sothat Sil's wards have impeded him, but the hound has Sunna'rah.

You must beat him to the prize - the reservoir that holds Vivec's stolen energy.

Vestige: Do you know where the Clockwork City is located?

Azura: Such knowledge has been hidden even from me, Mortal. But I know someone who can provide you with the means to travel to Sotha Sil's creation.

Stand back and I shall summon the mage of cogs and gears.
Even to Azura, one of the eight most powerful Daedric Princes, the location of the Clockwork City is hidden.
Morrowind Online said:
Barilzar: So Sotha Sil's forgotten tool was modified to steal Vivec's energy, which in turn energized the Clockwork City. Lit it up like the top of Red Mountain. Even Vile's dog would be able to see that!

Vestige: Can you get me to the Clockwork City or not?

Barilzar: What is Barbas after? Wait, gears click into place...the reservoir! You need to reach the reservoir that contains Vivec's stolen energy before Barbas! I can get us to the entrance in Seht's Valt, beneath the Mournhold Temple. Ready to go?
Vivec's divine energy was used to energize the entire Clockwork City and light it up. It was so bright that it was seen across universes and dimensions, which is how Barbas found it. Keep in mind that the Clockwork City is infinite in size (as said above), so it would take infinite energy to light it up (also said above).
Sotha Sil reshapes the Mundus from the Clockwork City.
New Story Expansion for The Elder Scrolls: Legends - Return to Clockwork City said:
Millennia ago, the tinkerer god Sotha Sil built himself a hidden sanctuary, from which to shape his vision of the future. He called it the Clockwork City, and it was there that he died, when a fellow god betrayed and murdered him.
Varieties of Faith Throughout the Empire said:
Sotha Sil (Mystery of Morrowind): God of the Dunmer, Sotha Sil is the least known of the divine Tribunal. He is said to be reshaping the world from his hidden, clockwork city.

Even way back in Morrowind, Vivec existed outside time. When he sleeps, or is even killed in the world of time, all he needs to do again is wake up and he's alive again, and no time has passed.
Morrowind said:
Vivec: It is like being a juggler. Things are always moving, and you learn to know where they are without even thinking about it. Only there are many, many things moving. And sometimes, like any juggler, you drop something. I'm afraid it has become a lot more a matter of dropping things lately. There's too much to do, and not enough time, and I'm losing my touch. Perhaps I'm growing old.

It is a bit like being at once awake and asleep. Awake, I am here with you, thinking and talking. Asleep, I am very, very busy. Perhaps for other gods, the completely immortal ones, it is only like that being asleep. Out of time. Me, I exist at once inside of time and outside of it.

It's nice never being dead, too. When I die in the world of time, then I'm completely asleep. I'm very much aware that all I have to do is choose to wake. And I'm alive again. Many times I have very deliberately tried to wait patiently, a very long, long time before choosing to wake up. And no matter how long it feels like I wait, it always appears, when I wake up, that no time has passed at all. That is the god place. The place out of time, where everything is always happening, all at once.
Morrowind said:
Vivec: I have no idea what happened to the Dwemer. I have no sense of them in the timeless divine world outside of mortal time. And, in fact, if I did believe they existed, I would be in no hurry to make contact with them. They may, with some justice, hold the Dunmer race responsible for their fate. My intuition is that they are gone forever -- and that is perfectly fine with me.,_Sermon_19
The 36 Lessons of Vivec said:
Vivec put on his armor and stepped into a non-spatial space filling to capacity with mortal interaction and information, a canvas-less cartography of every single mind it has ever known, an event that had developed some semblance of a divine spark. He said, 'From here I shall launch my attack on the eight monsters.'
Dagoth Ur also thinks outside time.'s_Plans
Dagoth Ur's plans said:
Dagoth Ur thinks on a large time scale -- for the most part, in the outside-of-time scale of the divine consciousness. He thinks that only obstacles of mythic scale are worth consideration. He believes he is fated to rule Morrowind, to free Morrowind of the Empire, and to become the new hard-loving Father of Morrowind. Given that perspective, the only opposing forces Dagoth Ur worries about are the Tribunal, the Daedra, the Emperor, and the Incarnate.

With the Tribunal's loss of Sunder and Keening, and with the diminishing resources of Vivec, Almalexia, and Sotha Sil, Dagoth Ur believes he has permanently gained a decisive strategic advantage. On a mortal timescale, the battle may last for centuries, but the outcome is not in doubt. And Akulakhan may be a device for dramatically reducing the time scale for a decisive victory.
Vivec exists in multiple universes simultaneously.
Michael Kirkbride said:
If a hermaphroditic, bug-armored, bipolar god-king existing in multiple universes who has his very own bible with *actual* magic strewn throughout it is your idea of a cliche, then I really would like to live in your world. It sounds fun and new.
Vivec battled a manifestation of Dagon. This is confirmed in the Morrowind Prima.

Aios, the AI who governs the substrata operations of the Clockwork City, classifies Almalexia as an existiantial threat level to the Clockwork City, along with the Numidium. Note that Nocturnal (as the Ur-dra no less) is just moderate.
Clockwork City said:

I am Aios, the Automata Incarnum Overseer System. Master sil created me to maintain and supervise the substrata operations of Clockwork City.
This partition can provide answers to class-seven queries only. Thank you for your understanding."
Vestige: Your master is in danger. Let us through so we can help him.
Aios: Assessing threats to Master Sil. Dreaming... open window. Sunlight through glass.
Threat analysis prepared: Prospect Numidium: negative. Prospect Almalexia: negative. Prospect Erasure: negative. No existential threat detected.
Vestige: There is a threat! The Daedric Prince, Nocturnal!
Aios: Accessing privatized threat-array. Dreaming... knee abrasion. Lullaby.
Threat located. Nocturnal. Ur-dra. Unfathomable Mistress of Shadows. Prospect registered. Risk level: moderate. Thank you for your concern.
And Almalexia did ultimately kill Sotha Sil (abet after the loss of his divine power).

In order for the Tribunal to ascend to godhood, it took the power of Keening and Sunder, powerful Dwemer artifacts that can alter the laws of reality.
Morrowind said:
Baladas Demnevanni: During the Dawn Era they researched the death of the Earth Bones, what we call now the laws of nature, dissecting the process of the sacred willing itself into the profane. I believe their mechanists and tonal architects discovered systematic regression techniques to perform the reverse -- that is, to create the sacred from the deaths of the profane.
Morrowind said:
Baladas Demnevanni: This is an explanation of how the Dwemer tried to make a new god, Anumidium, using Kagrenac's tools and the sacred tones on Lorkhan's Heart. It has several interesting theories about how to bend the Ehlnofey or "Earth Bones," but I am not entirely sure I understand it myself. Perhaps after another century of study I could have a better answer for you.
Morrowind said:
Baladas Demnevanni: As the books and other artifacts in Dwemer ruins rarely show signs of wear or age, I believe that the Dwemer knew of a preservative effect, perhaps a device still active which denies or controls the Earth Bones governing time and decay.
And if you want a validation for The 36 Lessons of you go.
ESO Live - The Influential Factions of Vvardenfell said:
Gina Bruno: Where did Vivec get his staff?

Lawrence Schick:
Muatra? It's not actually...It's a spear actually...and need to read his 36 Lessons and will find out more about Vivec's spear than you want to know.
There's more in terms of hax, but in terms of power, I think it's pretty clear how strong the Tribunal are. In their prime, Sotha Sil created the Clockwork City, a reality of infinite extent outside space and time in interdimensional space that's a Manifest Metaphor, which is capable of remaking or destroying the entire Mundus. Vivec's divine energy lit up the entire Clockwork City, and Almalexia is considered an existential threat to it. When Nocturnal engulfed the Clockwork City, Sotha Sil banished her when he regained his full power. The Heart of Lorkhan and it's duplicate the Mechanical Heart bestow infinite energy to it's user, and a normal mortal cannot withstand its power without being destroyed. Yet the Tribunal withstood its power for thousands of years, as did Dagoth Ur and the Sixth House (though the later for centuries, not millenia). Even when weakened, the Tribunal held back the power of Dagoth Ur for centuries before the Heart of Lorkhan vanished. Gaining power from the Heart of Lorkhan or removing it involved altering the laws of reality themself. At minimum, the Tribunal are universal+, though they could be a lot higher (multiversal+ or beyond).