Tunnels are used for transportation, mining, and drainage purposes, as well as for installation of power sources. Although tunneling is difficult and dangerous, the benefits are often worth the effort. Early civilizations relied on tunnels to transport water for drinking and irrigation. The Egyptians tunneled into cliffs to construct temples, and in 2100 B.C., the Babylonians went so far as to build a pedestrian tunnel under the Euphrates River by diverting the river during the tunnel's construction. The Greeks and Romans practiced tunneling extensively, the Romans constructing aqueduct tunnels through mountains.

Tunnel technology went through a long hiatus until about the 1700s, when tunnels were included in the development of canal networks in Europe and North America. The use of gunpowder blasting in excavations of solid rock was a major advance; different explosives are used today, although the blasting method is still similar. As railroads gained prominence beginning...