It would make sense to have parts of it be hollow. I would think that would save a ton of labor (or many thousand tons.)
https://freerepublic.com/tag/jeanpierrehoudin/index?tab=articles
https://www.youtube.com/watch?v=aGV1EQ-xx-M
https://www.youtube.com/watch?v=3NCK99mQUxw
https://www.youtube.com/watch?v=eGqfdXkAQMk