Roman roads Part 2
Many Roman roads have survived to the present day, and this is the best evidence that their construction was approached thoroughly and with all due diligence. In other places the time didn't spare the creations of the ancient builders, but where once marched the legions of the paved modern highway.
These paths it is easy to find on the map highway, running along the route of the Roman, generally almost perfect straightness. Which is not surprising: any "hook" would lead to a serious loss of time for the Roman troops, moving mostly on foot.
European Antiquity knew nothing of the compass, and cartography in those days was in its infancy. Nevertheless and this cannot fail to impress the Roman surveyors and managed to lay almost perfectly straight tracks between settlements, separated from each other by tens and even hundreds of kilometers.
"Thunder" was one of the main and the most advanced techniques of Roman surveyors and was a vertical metal rod with a pointed lower end for sticking into the ground.
The top end was crowned by a bracket with the axis on which were planted by a horizontal crossbar. With each of the four ends of the cross hanging threads with weights. Construction of the road began with the fact that the surveyors have placed pegs along the line (rigor), which is a future route. Thunder helped to build three peg along the same line, even if they were not simultaneously in line of sight (for example, due to the elevation).
The other purpose of the thunders the carrying out of excavation area perpendicular to the lines (which actually needed the pad). Surveying work was carried out literally "in the eye" the field of view of the thread of the plummet and standing in the distance of the pegs, the engineers were checking to see if the pegs deflected from the vertical axis and whether they are built in a straight line.
Of course, not all roads that were part of the huge communications network of Ancient Rome, was distinguished for the same quality. Among them was the usual dirt trails, gravel, and the Causeway of sand covered with logs. However, a real masterpiece of Roman engineering became famous via public paved road, built by technology, survived for millennia. Their mother was the famous Appian way.
The Roman technology of road construction elaborates a prominent architect and engineer of Antiquity, Marcus Vitruvius Pollio a (I century BC). Via the construction began with the fact that along the future route at a specified distance (2.5-4.5 m) broke two parallel grooves. They noted the working space, and at the same time gave builders an idea about the nature of the soils in the area. In the next stage the soil between the grooves is chosen in the long trench. Its depth is dependent on topography and geological characteristics, as a rule, the builders tried to get to the rock or to more solid soil layer and can be up to 1.5 m.
Then the road was built by the method of "layer cake". The bottom layer was called (support) and consisted of large rough stones the size of about 20 to 50 cm, the Next layer was called the (gravel) and were a mass of smaller broken stone, bonded with a binder solution. The thickness of this layer was about 20 cm in the Composition of the Roman concrete has varied depending on location, but in the Apennine Peninsula as the solution most often used a mixture of lime with ground volcanic rock that contains silicate of aluminum.
This solution showed properties setting in water and after hardening was distinguished by water resistance. The third layer is the nucleus was thinner (about 15 cm) and consisted of cemented small fragments of brick and ceramics. In principle, this layer could be used as a road surface, but often on top of "kernel" put the fourth layer. In the vicinity of Rome for the pavement are usually used large boulders of basaltic lava. They had an irregular shape, however, they were hewn so they fit tightly to each other.
Small irregularities of the pavement leveled with cement mortar, but even the most well preserved roads, this "grout" in our days disappeared without a trace, exposing the polished stones. Sometimes for the creation of pavement was applied and the stones are correct, for example rectangular, of the form they, of course, it was easier to adjust to each other.
The pavement had a slightly convex profile, and falling on her rain water stood in puddles, and dripping in running along both sides of the road drainage grooves.