It has always been harder to build a structure underground than in the open air. Despite that, people have created underground structures for a very long time, achieving great
feats. This was particularly true in ancient times, when there were no pumps to drain the water which would seep into the tunnels, swamping them. There were no fans either to artificially refresh the air, nor powerful lighting or boring equipment. Above all, the biggest challenge was following the right direction without topographic sighting instruments.