Outside of just looking cool ,I never understood the reason to have a floating city, the amount of energy and all the backup systems needed must have been staggering.
SPOCK: Stratos, Captain. A city actually floating in the sky.
SPOCK: Remarkable. The finest example of sustained antigravity elevation I've ever seen.
Obviously Spock thinks that floating cities are very rare. Stratos might even be unique in known space. But Spock says nothing about the energy demands needed for Stratos.
Hence the miners having to spend their lives digging in the caves to keep the city a floating!
JB
Possibly the Troglodytes on the surface are not all miners. They may work in many different occupations to keep themselves and their masters fed and clothed and housed, etc., etc. And they may mine a lot of other minerals beside zenite, which as far as I know has only one use, to cure plant plagues.
But why do they say the zenite gas in the mines affects all the Troglodytes? Because they live in underground communities for reasons of efficiency and shelter from harsh surface conditions. Just as the great underground city of Moria (attached to mines) was called the Mines of Moria in Lord of the Rings, the underground community of the Troglodytes (attached to mines) is also called mines. And no doubt the atmosphere in the underground community is contaminated by zenite gas leaking from the zenite mines.
Anyway, the labor of the Troglodytes does a lot more than merely keep Stratos floating in the air.
Whether the floating system consumes energy or requires maintenance, or is based on something passive like magically floating zenite crystals, is not established. But gravity-manipulating technology in Trek is dirt cheap and reliable, with primitive 1990s Earth spacecraft and alien machines hundreds of thousands of years old being equally adept at maintaining it, seemingly indefinitely.
From the looks of it, Stratos floats because it can - the tech awes Kirk and Spock, which is the likely point for its existence.
Timo Saloniemi
One reason for Stratos to float could be to keep the city dwellers in and the Troglodytes out, and thus keep the society on Ardana "stratified".
But the main and original purpose was probably to keep away from the harsh conditions on the surface of Ardana.
SPOCK: The surface of the planet is almost unendurable. To restrict a segment of the population to such hardship is unthinkable in an evolved culture.
VANNA: Centuries ago, Stratos was built by leaders that gave their word that all inhabitants would live there. The Troglytes are still waiting.
Presumably Vanna meant that the Troglodytes were promised that they could live in the comfort of Stratos and commute to work on the surface and in the mines. Maybe even that they would live and work on Stratos.
SPOCK: But they're all the same species. Those who live on Stratos and those who live below all originated on the planet. Their physical and mental evolution must be similar. That is basic biological law.
MCCOY: That's true, Spock, but obviously the ancestors of those who live on Stratos removed themselves from the environment of the mines. Therefore they avoided the effects of certain natural growths.
This implies that MCCoy believes, accurately or not, the natives of Ardana all lived underground in what he loosely calls "mines", probably for protection against harsh surface conditions, long before Stratos was built.
I suspect that Ardana had a very small population and then most of the population was exterminated by alien conquerors, with a small number kept to work the mines. The aliens left Ardana and left some of their technology behind. Inspired by the alien antigravity technology, the Ardanans built Stratos and then the elite broke their promise and kept the troglodytes in the mines, according to Vanna's version. Or maybe the aliens built Stratos and the elite of Ardana simply moved into it and continued to oppress the rest as they had been oppressed by the aliens.
Or maybe the aliens moved the Ardanan elite into Stratos where they administered the mines for the aliens, and could live a good life as long as they could keep the Troglodytes working and the ore flowing, so that the quota would be ready when the aliens came to pick it up. And then for some reason the aliens stopped coming for the ore and the Ardanan elite gradually began to work for themselves.
PLASUS [on monitor]: How can a mere filter accomplish what centuries of evolution have failed to do?
KIRK: Doctor McCoy has analysed the zenite thoroughly. We've checked his findings through the computer and they're absolutely valid.
PLASUS [on monitor]: And do your computers explain how my ancestors, who also dwelt in caverns, evolved sufficiently to erect Stratos while the Troglytes did not?
SPOCK: Unequal evolution did not begin until after your ancestors removed themselves from constant exposure to the gas, Mister Advisor.
PLASUS [on monitor]: Preposterous.
There does seem to be a bit of chicken and egg situation here. If Ardanans can't escape from the dumbing down effects of zenite gas without living in Stratos, and if the Troglytes affected by the zenite gas could never have built Stratos, how could the ancestors of Plasus have built Stratos while being exposed to zenite gas before they lived on Stratos?
This seems like strong support for my theory that aliens built Stratos and the Ardanan elite later moved into Stratos without building it themselves.
SPOCK: But they're all the same species. Those who live on Stratos and those who live below all originated on the planet. Their physical and mental evolution must be similar. That is basic biological law.
MCCOY: That's true, Spock, but obviously the ancestors of those who live on Stratos removed themselves from the environment of the mines. Therefore they avoided the effects of certain natural growths.
Spock and McCoy agree that all the Ardanans, Stratos dwellers and Troglodytes alike, originated on the planet Ardana, and their viewpoint is likely to be fair and unbiased and based on scientific evidence.
But Plasus, the High Advisor to the Planet Council of Ardana, says:
PLASUS: Troglytes are not like Stratos dwellers, Mister Spock. They're a conglomerate of inferior species. The abstract concepts of an intellectual society are beyond their comprehension.
So Plasus claims that the Troglytes are not the same species as the Stratos dwellers despite their obvious external similarities. And this is probably just some excuse that the Stratos dwellers have made up in an attempt to justify their treatment of the Troglytes.
But I suppose there is a chance that Plasus is correct. Perhaps the Troglytes are descended from aliens tricked into coming to work on Ardana with a false promise they would get to live in Stratos when it was finished.
