New tunnel building technique

[LONDONER]

Adhesive was not necessary when you did the job well. The typical Roman arch and other similar constructions were held in place simply by fitting the stones to each other. Some of those constructions still stand. Granted, tunnels are different.

I see no difference between tunnels and bridges. The fact is that the more weight applied, the stronger they become. I have seen an example of an arch in Morocco built by Phoenicians over 3,000 years ago.