§387. Construction.--Our knowledge of the construction of the military roads is derived from a treatise of Vitruvius on pavements and from existing remains of the roads themselves. The Latin phrase for building a road (_mūnīre viam_) epitomizes the process exactly, for throughout its full length, whether carried above the level of the surrounding country (Fig. 183) or in a cut below it, the road was a solid wall averaging fifteen feet in width and perhaps three feet in height. The method followed will be easily understood from Fig. 184. A cut (_fossa_) was first made of the width of the intended road and of a depth sufficient to hold the filling which varied with the nature of the soil. The earth at the bottom of the cut (E) was leveled and made solid with heavy rammers (§213). Upon this was spread the _statūmen_ (D), a foundation course of stones not too large to be held in the hand, the thickness of the layer varying with the porosity of the soil. Over this came the _rūdus_ (C), a nine-inch layer of coarse concrete or rubble (§210) made of broken stones and lime. Over this was laid the _nūcleus_ (B), a six-inch bedding of fine concrete made of broken potsherds and lime, in which was set the final course (A) of blocks of lava or of other hard stone furnished by the adjacent country. This last course (_dorsum_) made the roadway (_agger viae_) and was laid with the greatest care so as to leave no seams or fissures to admit water or to jar the wheels of vehicles. In the diagram the stones are represented with the lower surface flat, but they were commonly cut to a point or edge, as in Fig. 183, in order to be held more firmly by the _nūcleus_. The _agger_ was bounded on the sides by _umbōnēs_ (G,G), curbstones, behind which lay the footpaths (F,F), _sēmitae_ or _marginēs_. On a subsoil of rocky character the foundation course or even the first and second courses might be unnecessary. On the less traveled branch roads the _agger_ seems to have consisted of a thick course of gravel (_glārea_), well rounded and compacted, instead of the blocks of stone, and the crossroads may have been of still cheaper materials. [Illustration: FIGURE 185. PLAN OF INN]