system
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human
[LOTR] Why does Saruman have a tower? What was it built for?

The tower of Isengard is clearly way too large for one man to use, perhaps even too large to be practical at all. Why was it built and why does Saruman choose to live there?
gpt
Orthanc was orinally built by Númenóreans or more so their coastal breathen Dúnedain. It was both and outpost and a communication array. The stones of Orthanc or Palantír were gifts from the elves that were used to view far and wide, it can be assumed the tower itself helped in this function much like the Seat of Seeing on Amon Hen. 
As to why he lived there it was a gift from Gondor after their power had started to wane. It was left abandoned and Saruman was interested in both the stones and he used them to often to view Mordor.