150

HISTORY OF ENGINEERING.

Rook I

vast sewers, winch, according to Pliny , ranked among the greatest works ever undertaken.The subterranean fosses, or continued bridges of great length and breadth, sustainedenormous weights, as columns, obelisks, and other pieces of stone, dally passing overthem. Pliny relates that when M. Scaurus wished to transport 360 marble columns,each 38 feet long, from the place where they had been used, in his theatre, to the PalatineMount, the inspectors of the sewers demanded some security to repair any damagewhich might occur. After Scaurus had completed his house, the sewers were examined,and found not to have sustained any injury ; they formed a portion of the roads under

Fig.1G2.

CARRIAGE ROAD.

which they passed, and were intended not only to effectually drain all that might be injuriousto health and cleanliness, but also to afford a better foundation.

Over these vaults was laid a bed, on which rested the materials forming the road, whichwas paved in the same manner as the bridges.

In Rome there were 31 principal streets, and about 422 lesser. According toPancerolus, one is mentioned as made by Heliogabalus from his palace, called PlateasAntoninianas, which was paved with stone or marble from Lacedaemon, of a beautifulgreen colour, mixed with porphyry.

The Materials used by the Romans for road-making were of two kinds; the stones whichformed the mass, and the cement which united them. According to Vitruvius , there werethree sorts of stone quarried, of different degrees of hardness. The soft, when first takenfrom the quarry, was easily cut and rendered useful for building purposes, and whenprotected from the weather, and not in contact with the ground, had considerable dura-bility.

That stone which sustained weight, andthe action of frost, without splitting, wasmostly used on the great roads, and wascalled Saxum or Silex.

In the formation of their roads, the Ro-mans used every kind of stone that couldconveniently be obtained; after the line wasset out, excavations -were made at thesides, from whence was extracted any ma-terial that was serviceable; and, establish-ing a solid and durable bed, by closing theground with iron rammers made for thepurpose, they spread the different stratawhich composed the area or mass of theroad. These were called statumen, rudus,nucleus, and surnraa crusta, which to-gether were in thickness about 3 feet.

In the great military roads, the statumenor lowest bed was formed of two coursesof flat stones laid in mortar : over this wasthe rudus, or rubble, well beaten; thenthe third layer, called the nucleus, a sortof beton , was spread; this w’as formed ofcoarse gravel and lime, used hot; on thiswas bedded the summa crusta.

When the road was carried over marshydistricts, a framework of carpentry was provided, called “ contignata paviraenta,” and the

Fig.1G3.

PLAN.