2 BULLETIX 220, U. S. DEPARTMENT OF AGRICULTURE. 
and at various other expositions and fairs. The models have also 
been displayed on road trains at all important places along the route 
of the Pennsylvania Railroad hi the State of Pennsylvania and along 
the entire system of the Southern Railroad, also along the St. "Louis 
& San Francisco Railroad, the Atlantic Coast Line, the Nashville, 
Chattanooga & St. Louis Railroad, and the New York Central & 
Hudson River Railroad. A comprehensive exhibit of these models, 
illustrating all standard types of construction, has been installed at 
the Panama-Pacific Exposition hi San Francisco, Cal. 
The models, as a rule, are constructed on a scale of 1 inch to the 
foot, so that each model is one-twelfth the size of the actual road 
which it represents. Modifications of the methods of construction 
may be necessary to meet local conditions. Advice and information 
relating to road construction, maintenance, or improvement in any 
section of the country may be obtained upon application to the 
Director of the Office of Public Roads. 
The descriptions of the models are so arranged in this bulletin as to 
present the historic development of road building. The Roman road 
is described first, and then descriptions are given successively of the 
French roads, after the ideas of the Romans and of Tresaguet, the 
roads of MacAdam and Telford, and finally the various types of 
modern construction. Among the latter are models showing brick, 
concrete, asphalt-block, macadam, sand-clay, gravel, and earth roads. 
There are other models showing the processes of maintenance, resur- 
facing, and bituminous macadam construction by the mixing and 
penetration methods. One model shows the various methods of 
draining and strengthening unstable foundations, while another 
shows a typical method of treating gravel or macadam roads to make 
them dustless and to prevent their disintegration under automobile 
traffic. Two models recently added to the series illustrate, respec- 
tively, road location and roadside treatment. 
,ROMAN ROADS. 
The Romans began building roads on a large scale more than 300 
years before the Christian era. The Appian Way, one of the most 
celebrated of their roads, was begun in 312 B. C, by Appius Claudius 
Caucus. This road led from Rome to Capua, a distance of 142 Italian 
miles. It was later continued to Brindisi, making the total distance 
360 miles. Rome continued as a great road-building nation for 
about 600 years, and fragments of some of its roads still remain. The 
Appian Way is said to have been in good condition more than 800 
years after its construction. 
The Roman construction was not uniform, though always extremely 
massive. The general form of construction employed during the 
