VIA APPIA ROSE 357 



to the essential cross-section. This explains why the number of long 

 tunnels built by the Romans is almost as great as the number of open 

 cuts. Among the outstanding examples of rock cuts, according to 

 Leger (^), is the one on the Appian Way, near Terracine, through a 

 cliff of marble perpendicular to the sea. This cut is 117 feet high, and 

 98 feet long. Upon the Flaminian Way, at the crossing of the Ap- 

 penines, Vespasian bored the tunnel of Furlo, which was about 984 

 feet long. 



The Eoman roadbuilders followed the passes across the mountain 

 ranges, and made the necessary development by means of switchbacks, 

 in order to attain elevation, but, unfortunately, they permitted exces- 

 sive grades of as much as 15 to 20 percent. In the early days, ap- 

 proach grades of 10 and 12 percent were common even at bridge 

 approaches in the level plain. Later, however, when the traffic in- 

 creased considerably, the Romans realized that these steep grades made 

 impracticable the hauling of heavy loads. Consequently, the pro- 

 vincial roads were built without heavy grades. 



Curves required rather large radii because of the long teams, some- 

 times composed of 10 horses driven two abreast. However, in order 

 to avoid deep cuts in sloping terrain the Romans were compelled at 

 times to use curves with short radii. Thus Leger (4) cites an ex- 

 tremeW dangerous curve, with a radius of 23 to 26 feet, in a rock 

 cut 11 feet wide, with an approach grade of 15 percent, located near 

 Annecy at the Saint Clair bridge. 



The Romans built many important embankments mainly from side 

 borrow. The courses were leveled and rolled, with stone rollers, or 

 rammed carefully. Some of these embankments are of considerable 

 height and length. For example, in the restoration of the Appian 

 Way across the Pontine marshes, the Emperor Trajan made an em- 

 bankment 39 feet in width, and 17l^ miles in length, intercepted by 

 a great number of bridges and arch culverts. Frequently high em- 

 bankments were flanked by retaining walls. Leger (4) refers to a 

 dike at Arricia, upon the Appian Way, which is 745 feet long, 41 feet 

 wide, and 43 feet in average height, between retaining walls of 

 peperino stone. 



As a rule Roman roads were distinguished by long tangents, 

 undulating profiles, and crowned surfaces. 



DESCRIPTION OF THE MODEL OF THE VIA APPIA 



In order to visualize the method of construction, cross-section, and 

 vehicular use of an outstanding Roman road, a model (pi. 1) of the 

 Via Appia was built for the Bureau of Public Roads, United States 

 Department of Agriculture, by its modelmaker, H. W. Hendley (pi. 

 3). The design and construction of this model was based upon 



