It also made me think if the same kinds of concerns could be applied to Lyria and her fortress. But I thought about it, and no. I doubt it. She's a sorceress living on a huge freaking planet where magic users are basically the only people who can travel around the whole thing, and she also has the ability to travel to other planets, even other universes and dimensions. She could get her labor from literally anywhere, like having the place be built by a tribe of mute demons who communicate telepathically and whose telepathy doesn't work on normal humans. Or she could make an army of golems or something to build it.
Even assuming she used local human labor, she has the power to reach into people's minds and erase their memories. Oh, and she has a machine that can inload new data; she could alter their memories if she needed to.
Regardless of where she got her labor, if she thought they would talk, and their minds were resistant to her powers, she could kill them as fast as blinking, and wouldn't even have to bury the bodies. Hell, if their minds were resistant to her powers during life, she could kill them, reprogram their minds, and bring them back to life. But she likes to "cheat," IE to use her own personal power as little as possible, so she would take the route that was easiest, IE labor from a long way away, possibly another universe.
Also, it's not like she'd need a lot of secrecy with the bare bones of the fortress itself. The physical building itself only takes up about and acre or two of land. But she used magical knowledge given to her by a Fae friend, and so the fortress is alive, it's a knowe. And that means it's bigger on the inside than it is on the outside. The inside expands to suit the whims of the people it houses, and could potentially house, feed, and clothe a few million people before it couldn't stretch anymore. And she would have had to do a lot of other modifications herself anyway. There are aspects to the fortress, not even counting the expansion, that no human laborers, wherever you got them from, could do - things only a powerful sorceress can do.
So no, she wouldn't need to kill anyone.
Crossposted from http://fayanora.dreamwidth.org