The Bible Almanac, J. I. Packer, Merrill C. Tenney, William White, Jr., editors, (Thomas Nelson Publishers, Nashville; 1980), p. 297
The Romans were prodigious road builders. They spent five centuries completing a road system that extended to every corner of their empire and eventually covered a distance equal to 10 times the circumference of the earth at the equator. This included over 80,000 km. (50,000 mi.) of first-class highways and about 320,000 km. (200,000 mi.) of lesser roads.
Before the Romans built a road, they conducted a survey. They could calculate distances to inaccessible points, run levels with accuracy, measure angles, and lay out tunnels and dig them from both ends with a vertical shaft. Road surveyors considered the slope of the land and questions of defense. Where necessary (as in the regions of Cumae and Naples), they cut tunnels through mountains with a skill that aroused admiration for centuries. Because Romans tried to build straight roads&md;often over hills rather than around them&md;slopes frequently were steep; 10 percent grades were common.
When building an important road, Roman engineers dug a trench the full width of the road and 1.2 to 1.5 mi. (4 to 5 ft.) deep. The roadbed was built up with successive layers of large and small stone and rammed gravel; sometimes there was a layer of concrete. Normally roads were surfaced with gravel, which might rest on a bed of mortar. Near cities, in places where traffic was heavy, or in the construction of an important road, engineers paved the surface with large, carefully fitted stones about 30 cm. (12 in.) thick and 45 cm. (18 in.) across.
The type of construction varied with expected traffic, terrain, and available materials. Mountain roads might be only 1.5 to 1.8 m. (5 to 6 fit.) wide, with wider places for passing. Main roads were 4.5 to 6 m. (15 to 20 fit.) wide. The Appian Way was about 5.5 m. (18 ft.) wide&md;wide enough for two wagons to pass [a]breast&md;and paved with basaltic lava.
Stone bridges were usually built where roads crossed streams. Such construction was possible because the Romans had concrete much like that in use today. To make lime mortar set under water and resist water action, the road engineers had to add silica to the mixture. The Romans had large quantities of volcanic sand (pozzolana), which had a mixture of silica in proper proportions.
Unfortunately, records do not tell us how long it took to build Roman roads or how large the road gangs were that built them. The Appian Way&md;"Queen of Roads" and forerunner of many other Roman roads on three continents&md;was begun in 312 B.C. as a road for use in the Samnite Wars. The 211 km. (132 mi.) to Capua must have been completed within about a decade. Ultimately, the Appian Way reached southward 576 km. (360 mi.) from Rome to Brundisium on the Adriatic Sea. The road system was gradually extended through the efforts of numerous Roman emperors. Agustus, Tiberius, Claudius, and Vespasian were among those who launched great road-building projects.
Some Roman roads have been used throughout the Middle Ages and into modern times. The Appian Way, on which Paul traveled to Rome (cf.