I have every Dark sun book, but its the first time I see this.
Its look like the Dark sun pilot. It was released way before the first DARK SUN boxset and its look like a mixe of Dark sun and normal D&D.
Notes: DDA2 "Legions of Thyatis" an Official Game Adventure. This module is a stand-alone sequel to DDA1 "Arena of Thyatis". It is designed especially for the DM who wants to sharpen his interactive skills. Recommended for 4 to 6 characters, levels 3-4. Includes fold-out color maps. The Thyatis and Alphatia boxed-set gazetteer "Dawn of the Emperors" is useful for setting background.
Requires Dungeons & Dragons Basic and Expert set rules.
Credits:
Name Credit
John A. Nephew Design
Jon Pickens Editing
Bruce Heard Product Manager
Gerald Brom Cover Artist
Gaye O'Keefe Typography
Dungeons & Dragons DDA1: Arena of Thyatis PDF
Wizards of the Coast
It's Party Time in Thyatis. . .
And simply everyone is going to the magnificent Villa Osteroplus, home of the wealthy old senator, Helenites. Raucous fun, exotic food, and even advanced betting on the upcoming Arena games are expected. Even adventurers just in from the outlands may meet the powerful here. So don your festive togas, for in Thyatis City there are important connections to be made and deeds to be done, duels to be fought and fame to be won.
This module is designed especially for the DM who want to sharpen his interactive skills.
Presenting the detailed layout of a Thyatian noble's mansion and maps of the multi-level Coliseum of Thyatis For four to six characters, levels 2-3 Brief guide to Thyatis legal system New optional class, the Rake Fast unarmed combat system, including disarming attacks Special appendix on creating Thyatian names Featuring the DM Guide to Winging it.
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The cover is also illustrated by Brom and looks familiar.
Cover
its like the same guy
It's look like Dark sun emerged from these two module. Like a ripe-off.
That mean, the basic idea creating Dark sun was about a gladiator setting, not a desert setting.
As for the art, Tim and Troy have both said that they were inspired by the art of Brom and built much of their creative work around already drawn paintings by Brom.
Gladiatorial combat in D&D is as old as the game. Greyhawk city has an arena in it. Waterdeep has an arena in it.
The Empire of Thyatis is a blend of the Roman Empire and the Byzantine Empire... with some other influences tossed in. I believe trying to link it as some sort of developmental proto-Dark Sun is misguided. I own both of those adventures, in paper form, so I have read them cover to cover. There are similarities to be sure but those Thyatis adventures only built off of hooks that were already hinted at in the Dawn of the Emperors boxed set.
That mean, the basic idea creating Dark sun was about a gladiator setting, not a desert setting.
Why would Dark Sun have to be exclusive one or the other. The creators of the setting have admitted they were strongly influenced by the John Carter of Mars books by Edgar Rice Burroughs. A world of arena combat, cultures alien (yet familiar) to Earth, the powers of the mind, in a vast planet-spanning desert, where the world is slowly dying.
You can read Princess of Mars on the Project Gutenburg for free. Read it and you will be stunned in the similarity... far more than the superficial similarities between that old adventure and Dark Sun.
Don't forget (maybe you didn't know it) but the D&D team and the AD&D team at the old TSR didn't coordinate their work almost at all. I would be certainly surprised if there was the link you are proposing purely because it would go against the way things were commonly done back then.