The history of tunnels
It has always been more difficult to build a structure under the ground than in the open air. In spite of the difficulties, people have been creating remarkable underground structures since the remote past.
This was particularly true in ancient times when there were no pumps to empty the water which seeped or flowed into tunnels, or ventilators to refresh the air artificially, or powerful lighting or tunnel driving equipment. Finally at the time it was very difficult to keep the tunnel in the right direction as there was no surveying equipment at the time.
History of tunnels is related here by Michel Marec, a senior engineer with a specialization in tunnels.