|CITS| Tutorial: Problem: Roman Infrastructure 1

Roman Construction and Infrastructure
Part 1: Construction Methods and Technology

Authors:
Eric Finnemore
Ben Gordon
Scot Johnson

April 17, 1997

1.0 Introduction
This report covers the architecture and construction methods of the Roman Empire. Rome was founded about 753 BC, and soon grew to be the capital city of the Roman Republic and later the Roman Empire. The Roman Empire lasted until 476 AD in the West, a span of years that saw the construction of some of the worlds finest and most durable architecture and civil works. The advancements and influences of the Romans can still be seen in modern construction techniques. This report will examine the general stages of Roman town construction, modeled on Rome, but most Roman towns followed the same pattern.

2.0 The Architecture and Buildings of Rome
When building a new town, the Romans tried to find the most advantageous site. A broad plain with good soil was ideal, often along a river or coastline. Locations with forests or quarries nearby made construction easier. Once a suitable location was found, the surveyors laid out the city plan.

2.1 City Plan
The Romans were the first civilization to have a set plan for cities, and their grid system is still used today in some communities. The center of every Roman town was the forum, the main public square. Everything else in the town was placed in relation to the forum. The surveyors used a device called a groma when laying out the town. It consisted of four plumb bobs suspended from the ends of sticks that were connected at right angles. The groma allowed the Roman surveyors to mark out lines at right angles to one another.

The first streets laid out were the kardo, running north-south, and the decumanus, running east-west. The kardo was usually 20 feet wide, while the decumanus was usually 40 feet wide. After the main two streets were laid out, secondary streets were marked parallel to the main streets, the north-south streets being called kardines and the east-west streets called decumani. Each was numbered, the same as a modern current street and avenue numbering system. Lots were surveyed and marked in the same manner as the roads. The basic measure of land was a square 240ft on a side. The usual city plan was formed by placing a secondary kardine or decumani every 5 lots, forming regular blocks. A variety of smaller roads and alleys were used for access to the interior of the blocks.

2.2 Building Materials
The Romans primarily used a variety of stone and earth materials in their construction. The main building stone for the early Roman years was tufa, a soft and brittle stone that was found extensively around Rome. It could be quarried with bronze tools, and came in a variety of colors which were often used decoratively. Being soft, the tufa often weathered poorly and had to be protected with a stucco covering. As construction technology progressed, other types of stone were used as they were discovered. Peperino stone was a mixture of volcanic ash, gravel and sand, harder than tufa and more fireproof. Travertine was stone consisting almost entirely of lime, even harder than peperino, but susceptible to fire. Silex was a very hard rock made of lava, but it was so hard that it was difficult to produce, so it was not used much in buildings.

The Romans cut these stones into rectangular blocks, two Roman feet square by four feet long. Walls were built from these stones, laid in alternating courses of headers and stretchers until the wall was complete. In most early Roman construction, mortar was rarely used, the blocks being so smooth it was not necessary.

This shows a small temple constructed with blocks of peperino. The seams in the walls are visible due to the lack of a covering, but the blocks are very smooth and the structure is obviously still in excellent condition. After the decline of the Roman empire, many of the Roman works were taken apart and the excellent raw material they contained was reused in local structures.

During the first century BC, a volcanic ash called pozzolana was discovered. This discovery allowed concrete to be made for the first time, consisting of the ash, lime, and broken fragments of stone. Pumice could be added to make a lightweight mixture. The discovery of concrete allowed the Romans to build vaults and domes, structures that needed a strong yet lightweight material that could be molded as desired. Pieces of broken pottery were also used in the concrete mix, since they were plentiful in Roman cities. Concrete walls were build similarly to the modern way. A lumber framework was put in place, then the concrete poured in a semi-fluid state. Once the concrete set up, the frames were removed. Another technique of wall building was two parallel thin stone walls, the space between being filled with rubble and concrete. This kind of composite structure gave great strength with less expensive stone usage.

This shows a wall, composed of small pieces of rubble concreted together, with a facing of more regular larger stones.

Kiln-baked bricks were used early in the empire for construction, but soon faded to use as facings or decorations. They were of amazing quality, hard enough to able to strike fire like piece of flint. Also the bricks found at the far reaches of the empire are of equal quality to those from Rome, showing the consistency of Roman imperial quality control.

The walls were usually faced with smaller stones or bricks set in concrete, covered by stucco or plaster. The stucco was a more utilitarian finish, while the plaster could be polished and colored with pigments. This slide shows small tufa blocks set in the walls as facings.

Marble, which was used widely by the Greeks, was rarely used for construction, being reserved for floors, walls coverings, and decorative figures.

The Romans used scaffolding extensively in their construction. The square holes used for the beams supporting the scaffolding can be found in most concrete fixtures and quarried into some of the stone blocks.

2.3 Technical Advancements
Besides their advances in materials, the Romans advanced the study of physics and engineering begun by the Greeks. The Romans understood gears and pulleys, and used them for mechanical advantage. One particular machine used men in a treadmill as the motive force to wind a rope and lift the object with a series of three pulleys.

The Romans also were able to harness the power of water to do work. Archeologists have found a mill built on the downslope of a hill next to a waterway at Barbegal, in what is now France. The water was diverted over a series of 16 waterwheels which were geared to mill stones. The facility is estimated to have produced enough flour to feed a city of 80,000 people with a minimal labor force.

The Romans also made advances in the livibility of buildings. This shows a heating duct that was unearthed in the wall of a house in Pompeii.

It is a clay pipe that transmitted heated air from a fire in one place into all the rooms of the house, forming an early central heating system.

2.4 Arches
In more complex structures, the Greeks had understood arches and vaults, but had not used them much since they lacked the material advances of the Romans. With the development of concrete the Romans began using arches and vaults almost exclusively, instead of the rectilinear practice of only vertical and horizontal members.

One of the most ambitions and innovative use of arches was in the Colosseum of Rome, more correctly known as the Flavian Amphitheatre. The Colosseum was built in 79AD and is still an amazing structure today. When intact it could seat up to 55,000 people in many different seating classes. Each layer of arches is supported by the next level. The circular configuration means that all the stresses are distributed into an essentially endless series of arches. The resulting outward pressures are relatively insignificant.

2.5 Vaults and Domes
The development of concrete made vaults such as this barrel vault possible. This vault is part of Trajan's Marketplaces, large open buildings built to provide space for businesses.

A more ambitious use of the vault is to make it into a dome, the best example being the Pantheon. The Pantheon was built between 118 and 128AD, replacing two earlier temples that had been destroyed by fire. It was the largest domed structure in the pre-industrial world. The picture shows the entrance to the temple.

The Pantheon was the first Roman structure to combine the new concrete technology, the dome in the background, with the decorative Greek style seen in the marble columns. The hemispherical dome rises 142 feet above the floor of the temple, forming an exact half of a sphere since the circular floor area is also 142 feet in diameter. The dome was supposed to represent the sky, with the circular opening representing the sun.

The dome is taller than some modern domes in state capitol buildings. The dome is 20 feet thick at ground level and tapers to only 90 inches at the top. The concrete composition also varies as the dome nears the top, replacing the heavier gravel mixture at the base with a pumice mixture that is much lighter yet sufficiently strong. The dome also has empty clay jugs embedded in it to further lighten it. The dome is supported by a double wall system, on a 15 foot thick concrete foundation. The walls were reinforced and connected together with internal arches. After the construction of the Pantheon, Romans used the dome in many places, and even used circular domes over rectangular rooms.