Xll INTRODUCTION 



to facilitate the illumination of this tunnel, its floor and roof 

 were made gradually converging from the ends toward the 

 middle ; at the entrances the section was 75 ft. high, while at 

 the center it was only 22 ft. high. This double funnel-like 

 construction caused the rays of light entering the tunnel to 

 concentrate as they approached the center, and thus to improve 

 the natural illumination. The tunnel is on a grade. It was 

 probably excavated during the time of Augustus, although 

 some authorities place its construction at an earlier date. 



During the Middle Ages the art of tunnel building was 

 practiced for military purposes, but seldom for the public need 

 and comfort. Mention is made of the fact that in 1450 Anne 

 of Lusignan commenced the construction of a road tunnel 

 under the Col di Tenda in the Piedmontese Alps to afford 

 better communication between Nice and Genoa ; but on account 

 of its many difficulties the work was never completed, although 

 it was several times abandoned and resumed. For the most 

 part, therefore, the tunnel work of the Middle Ages was in- 

 tended for the purposes and necessities of war. Every castle 

 had its private underground passage from the central tower or 

 keep to some distant concealed place to permit the escape of 

 the family and its retainers in case of the victory of the enemy, 

 and, during the defense, to allow of sorties and the entrance 

 of supplies. 



The tunnel builders of the Middle Ages added little to the 

 knowledge of their art. Indeed, until the 17th century and 

 the invention of gunpowder no practical improvement was 

 made in the tunneling methods of the Romans. Engravings 

 of mining operations in that century show that underground 

 excavation was accomplished by the pick or the hammer and 

 chisel, and that wood fires were lighted at the ends of the 

 headings to split and soften the rocks in advance. Although 

 gunpowder had been previously employed in mining, the first 

 important use of it in tunnel work was at Malpas, France, 

 in 1679-81, in the tunnel for the Languedoc Canal. This 



