The key to creating and maintaining the Roman Empire was its roads, which would be a marvel of engineering even today.
It is hard to wrap your head around how much of the world ancient Rome once controlled. The Roman Empire began in the north at Hadrian's Wall in Scotland, and extended south to Morocco. It extended from the Rhine River in Germania to Egypt, and eastward all the way to the Euphrates River in Mesopotamia.
The Roman Empire Source: George R. Crooks/Wikimedia Commons
The way Rome administered this vast empire was through its roads, or viae Romanae. Roman roads allowed the movement of armies, public officials, and goods – lots and lots of goods.
The expression, 'All roads lead to Rome' apparently was true as 29 military highways radiated out from Rome. The empire's 113 provinces were connected by 372 roads which covered more than 250,000 miles (400,000km), and 50,000 miles (80,500km) of them were paved with stones.
Roman roads in Italy Source: Agamemnus/Wikimedia Commons
Roman roads survived for thousands of years, and many of them have been paved over and become the major highways of today. The most famous, and one of the earliest Roman roads, was the Appian Way which connected Rome to the city of Brindisi in southeast Italy. The Appian Way was built in 312 BCE and it was named for a Roman official named Appius Claudius Caecus.
Roman roads in Britain Source: Wikimedia Commons
The Itinerary of Antoninus
The Itinerary of Antoninus was created around the third century, and it mapped the stations and distances along various Roman roads. Measurements were in Roman miles which were equal to 0.92 miles (1,480m).
The Itinerary of Antonius stated, "There is hardly a district to which we might expect a Roman official to be sent, on service either civil or military, where we do not find roads. They reach the Wall in Britain [Hadrian's wall]; run along the Rhine, the Danube, and the Euphrates; and cover, as with a network, the interior provinces of the Empire."
Roman roads in Spain Source: Redtony/Wikimedia Commons
Roman road construction
Roman road construction began with a civil engineer who proposed where the road should be placed. Then, the agrimensores went to work surveying the roadbed. They used two devices, the rod and the groma, which allowed them to measure precise right angles.
Groma Source: MatthiasKabel/Wikimedia Commons
Next, the gromatici placed rods and laid out a grid pattern on the plan of the road. Following them were the libratores who began digging the road using ploughs. They excavated the roadbed down to the firmest ground they could find.
Next, rubble, gravel, and stone were laid down and tamped down in a process called pavire, or pavimentare. Finally, polygonal-shaped or square-shaped paving stones were set in a lime-based concrete, which the Romans invented. Finally, the entire roadway was angled for drainage.
Some Roman roadways were cut through hills while others spanned rivers or ravines. The Romans built bridges using the arch as their basic structure, and they were so well constructed that many are still in use today. Roman road construction was commemorated in a frieze on Trajan's Column in Rome.
Frieze on Trajan's Column Source: Wikimedia Commons
The Law of Twelve Tables which was written in around 450 BCE required that any public straight Roman road be eight Roman feet wide, or 7.78 feet (2.37m) wide, and that it be twice that width if curved. In rural areas, Roman roads had to be 12 Roman feet wide in order to allow two carts to pass one another.
Roman law established road access across private land, and within Rome itself. It restricted commercial carts to night-time use only within the walls of a city and within a mile (1.6km) outside of the city's walls.
A Roman road preserved at Pompeii Source: Paul Vlaar/Wikimedia Commons
Roman milestones
Dotted along Roman roadways were Miliarium, or milestones. They appeared along the Appian Way before 250 BCE, and by 124 BCE, milestones appeared along most Roman roads.
Roman milestone Source: Wikimedia Commons
The modern word 'mile' comes from the Latin milia passuum, or "one thousand paces". This equalled 4,841 feet (1,476m). Roman milestones were cylindrical columns 20 inches (51cm) in diameter, standing 5 feet (1.5m) tall, and weighing more than two tons.
At their base was inscribed the number of the mile relative to the road it was placed on, and in a panel at eye height was the distance to the Roman Forum and information about who had commissioned, constructed, or repaired the road.
A really big road map
If you've got a really big room, you can see the entire Roman road network in a copy of The Peutinger Map. It is a 13th-century parchment copy of a map of Rome's entire road system that was prepared by Emperor Augustus's friend, the general Marcus Vipsanius Agrippa who died in 12 BCE.
Section of the Peutinger Map Source: Bibliotheca Augustana/Wikimedia Commons
The Peutinger Map includes Europe, (excluding the Iberian Peninsula or the British Isles), North Africa, the Middle East, Persia and India. It also shows the town of Pompeii, which was destroyed in 79 AD by the eruption of Mount Vesuvius. The Peutinger Map is one foot, one inch (33cm) in height, but is 22.1 feet (6.75m) long, hence it needs a really big room.
Mansiones, tabernae and mutationes
Growing up alongside Roman roads were inns, or mansiones, which were located 16 to 19 miles (25 to 30km) apart. Tabernae, or taverns, provided refreshment, and soon new towns were springing up alongside them.
Mutationes were located every 12 to 19 miles (20 to 30km) along Roman roads, and they provided wheelwrights, cartwrights and veterinarians to travellers.
A mail service, the Cursus publicus, which was created by Emperor Augustus carried the regular mail of the empire, but for those who could afford it, there was a separate mail service called the tabellarii that employed slaves.
The infrastructure, including its roads, that ancient Rome created was not duplicated until the modern era – a truly amazing feat.
This article was written by Marcia Wendorf and first appeared in Interesting Engineering.