Tower of Trials was one of the three Sovereign level Treasures in the academy.
It was found by Alex Xander, the first Sovereign of Humanity in the Trios Ruins, also known as Earth Ruins.
It would create phantoms replicating the strength of those that entered it and was perfect to gain combat experience against other humans.
Alex Xander generously donated the wonderful treasure for the training of future warriors. Many decades after his contribution, the treasure became a cornerstone of Imperial Defense Academy.
It was a commonly acknowledged fact that Artifacts were beyond the level of a Sovereign.
Even the leading power in the cutting edge of star treasures, Trade Union could not forge a single Sovereign Treasure.
In fact, even creating a Level 9 treasure was incredibly hard.
Thus, the only Sovereign Treasures humans had were those from the Ruins.