So great is the difference between hard-rock and soft-ground tunneling
that they constitute two almost separate branches of the field. In
penetrating ground lacking the firmness or cohesion to support itself
above an opening, the miner's chief concern is not that of removing
the material, but of preventing its collapse into his excavation. The
primitive methods depending upon brute strength and direct application
of fire and human force were suitable for assault on rock, but lacked
the artifice needed for delving into less stable material. Roman
engineers were accomplished in spanning subterranean ways with masonry
arches, but apparently most of their work was done by cut-and-cover
methods rather than by actual mining.
Not until the Middle Ages did the skill of effectively working
openings in soft ground develop, and not until the Renaissance
was this development so consistently successful that it could
be considered a science.