X INTRODUCTION 



masonry, having interior dimensions of 12 ft. in width and 15 

 ft. in height. 



Only hand labor was employed by these ancient peoples in 

 their tunnel work. In soft ground the tools used were the 

 pick and shovels, or scoops. For rock work they possessed a 

 greater range of appliances. Research has shown that among 

 the Egyptians, by whom the art of quarrying was highly de- 

 veloped, use was made of tube drills and saws provided with 

 cutting edges of corundum or other hard, gritty material. The 

 usual tools for rock work were, however, the hammer, the chisel, 

 and wedges; and the excellence and magnitude of the works 

 accomplished by these limited appliances attest the unlimited 

 time and labor which must have been available for their ac- 

 complishment. 



The Romans should doubtless rank as the greatest tunnel 

 builders of antiquity, in the number, magnitude, and useful 

 character of their works, and in the improvements which they 

 devised in the methods of tunnel building. They introduced 

 fire as an agent for hastening the breaking down of the rock, 

 and also developed the familiar principle of prosecuting the 

 work at several points at once by means of shafts. In their 

 use of fire the Romans simply took practical advantage of the 

 familiar fact that when a heated rock is suddenly cooled it 

 cracks and breaks so that its excavation becomes comparatively 

 easy. Their method of operation was simply to build large 

 fires in front of the rock to be broken down, and when it had 

 reached a high temperature to cool it suddenly by throwing 

 water upon the hot surface. The Romans were also aware 

 that vinegar affected calcareous rock, and in excavating tunnels 

 through this material it was a common practice with them to 

 substitute vinegar for water as the cooling agent, and thus to 

 attack the rock both chemically and mechanically. It is hardly 

 necessary to say that this method of excavation was very severe 

 on the workmen because of the heat and foul gases generated. 

 This was, however, a matter of small concern to the builders, 



