Hearing the Elder's words,
Ian drew in a sharp breath. One of the great taboos of Time Travel was bringing back items that did not belong to one's own time and space! It could trigger unforeseeable causal chaos!
As everyone knew,
Time Travel had many taboos.
First, one could not interfere with or alter known major historical events, or it might cause the Timeline to collapse or reality to be reconstructed. Second, one could not meet one's past self—an encounter between one's past and future "selves" could trigger a mental breakdown, energy conflict, or a Time Paradox.
One could not travel repeatedly to the same point in time, could not save the dead, could not create a time loop, could not peer into or alter one's own Destiny—and bringing future technology, weapons, or knowledge back to the past could cause a Technological Explosion, an imbalance of power, or a distortion of history. Likewise, one could not bring things from the past into the future.
These were the taboo rules of Time Travel, truths acknowledged by countless alchemists. Yet the Elder before him had clearly done far more than merely violate several taboos.
It was not just that he had brought things back.
He had also traveled to the same time more than once and crossed paths with his past wife. Moreover, all of the other man's Hard Work had ultimately been aimed at accomplishing that eternal taboo.
The dead could not be saved.
If all the other taboos had already been shaken, then honestly, it was hard to say whether this taboo might also be shaken and fulfilled. It was likewise one of Albus Dumbledore's goals.
"But one of the taboos of Time Travel is that you cannot bring back items that do not belong to this time and space!