Complex sentence: Although the original site was at a higher elevation than the surrounding countryside, it was further modified through extensive filling and leveling, by one estimate half-a-million to 2 million cubic meters of earthen fill were needed, moved by the basketload.
Split into simpler sentences: Although the original site was at a higher elevation than the surrounding countryside, it was further modified through extensive filling and leveling. It was built on half-a-million to 2 million cubic meters of earthen fill, moved by the basketload.