SURVEYING AND ENGINEERING IN ANCIENT ROME
Ferris State University College of Technology Surveying Engineering
Roman monuments stand to this day as a testament to the greatness of Roman society. Some of the most distinctive monuments are the roads and aqueducts. These structures are impressive in their design and functionality, some of which can still be used today. These monuments also stand as a testament to those who built them. The surveyors of Rome played an essential role in the construction of the roads and the aqueducts, and developed many of the fundamental principles of surveying and construction. In this paper, we will examine the terms, definitions and units of measure used by Roman surveyors, look a the equipment used by Roman surveyors, and discuss how Roman surveyors used this equipment to lay out control for the building of roads and aqueducts.
LEARNING THE ROPES
The first step in understanding the methods of surveying in ancient Rome is to become familiar with the terminology, definitions, and units of measure that were used at the time.
Although surveying is one of the oldest professions, land surveyors of ancient Rome, the agrimensores, worked in a time of early techniques in land development. Land division was often undertaken in order to provide a place to live for veterans of the Roman army. These settlements were known as colonia.
One prominent way to developing land into tracts was known as limitatio. This technique involved creating a grid system of limities -- paths whose used varied. These limities were indexed by a set of master orthogonal axes, the kardo maximus (KM), and the decumanus maximus (DM); the latter was typically depicted vertically on a map, or forma. 
In recording the surveys, the forma was oriented based on calls that let the agrimensore know where he was in relation to the intersection, also known as a tetrans, of the kardo maximus and the decumanus maximus. The calls were as simple as: "above or below the KM, ultra kardinem and citra kardenem, respectively, and to the left or to the right of the DM, sinistra decumani and dextra decumani, respectively." These calls were marked in the field with termini that were essentially stone property corners. 
With the forma and termini, the agrimensore had a rough way to orient himself within the colonia. Another simple way for the agrimensore to orient himself was the indexed limities, the limes quintarius. These were typically every fifth limes, the more commonly used paths, or possibly ditches known as novercae. Tracts, or centuries, were demarked by boundaries known as fines. This process of dividing the land, known as deductio, was simply the act of colonization. 
Along with the agrimensore, there was another individual known as the mensore, or measurer. It was the mensore's job to aid the agrimensore in the division of the land. Land, to the Romans, was known as ager. Ager within the territorium, land under the control of a Roman city, was generally classified as ager arcifinius, unsurveyed land, or ager publicus, public land. 
The Romans developed forms of measurement to account for length and area. These units were simple and could be measured by a mensore without any form of measuring device. For example, the digitus, about 18.5 mm, was taken as the width of a finger. The minor palmus was nothing more than the width of the palm, or four digitus. The cubit, or cubitus, was the distance from the end of the fingers to the elbow, roughly 1.5 feet or 24 digitus. 
To measure longer distances, the feet of the mensore were used. A pes was the length of their foot. The pace, or passus, was a distance of roughly five feet. An actus was considered 24 passi and a stadium was 125 passus. For longer distances the mille passus or mille passus, meaning 1000 passus (also 625 stadia) was used. 
An actus, or 24 passus, was used as a common length and width in area demarcation. One square actus was equivalent to 14,400 pes. Other terms for areas included the iugerum, two square actus, the heredium, which equated to two iugerum, and the centuria, which was equal to 100 heredia. Interestingly enough, if the agrimensore found an error in an older survey which resulted in a gap, this land was deemed subsecivum, or unallocated, and was left alone. 
The following is a brief synopsis of Roman numerals:
I = 1 V = 5 X = 10 L = 50 C = 100 D = 500 M = 1000
Upon examination, two things stand out. First there was no concept of numbers smaller than one. Precision and accuracy are apparent in Roman work, but there was no need for the type of accuracy common to modern surveying.
The other accommodation not made with this numbering system is that 1000 is the maximum number. There apparently was no consideration made for numerical values exceeding this amount, yet another aspect of modern surveying not seen here.
All in all, the system of numbers and measurement was simple, but efficient, as demonstrated by some of the Roman structures that still stand today.
STRETCHING THE ROPES
Essential to every engineering project, presently as well as in ancient times, was the need for consistency and precision in measuring. The use of measuring equipment assisted the surveyors in this endeavor and was essential in the Romans' ability to build on a grand scale. Some methods were less precise than others, ranging from the use of pacing and ropes to standardized rods. The Romans also had several devices at their disposal that utilized the fundamental principals of surveying. These included the Groma, the Dioptra and the Chorobates.
The normal method or device used for measuring distances was the cord, which may have been made from a variety of fibers. The most common cord was the scoinion, which formed from twisted rushes or other similar substances. Also noted by the Greek philosopher Hero was the chain, but it is thought that it was not used as much as the cord due to its high cost and weight. Special attention is called to the fact that throughout history the cord-stretchers played an important part in society, especially in Egypt. The cords were kept stretched to help eliminate errors in measurements due to shrinkage or tension. Since land was taxed by area, correct measurements were very important. 
An alternative to the cord, which was used commonly by the Romans, was the measuring rod or kalamos. Originally it was made out of reed but it was typically made of wood. The original length of the rod was 5 or 6 2/3 cubits. The 6 2/3-cubit length was also known as the akaina, which corresponded to the wooden ten-foot rod (decempeda or pertica). On the end of the rod were bronze ferrules marked in digits for small measurements and flanged to abut neatly against its neighbor. The rod was a much more accurate measurement device since the wood expanded and contracted much less than the cords. 
For very long distances, pacers or bematisai were used. Notes were made of pacers traveling with Alexander the Great during his campaigns. It was the bematistai's job to count their paces and note their direction as they marched. Records and outline maps were compiled and published from the descriptions of these routes.
Temples, town grids and land boundaries needed to be laid out by Roman surveyors. These needed to be set in a particular orientation. The Romans used celestial bodies to establish an approximate North/South line. The sun was the most common star used, by observing the shadow of a vertical gnomon and marking the points where it appeared to be the longest. 
Relatively small set squares were also used by Roman surveyors. These squares could be laid on the ground and by extending the cords from the stakes could be placed. Once a rectangle was formed, the resulting diagonal distances could be compared against each other to check for squareness. 
The surveyors recorded their field measurements on wax tablets or papyrus. The abacus may have been used to do complex mathematical calculations. The properties of the 3, 4 and 5 triangle were well known and multiples could be tied in a rope or cord for laying out right angles. 
The Roman Groma was an instrument used for alignment. It consisted of a pole, roughly five feet in length, with a pointed foot or ferramentum. At the top of the pole was a rotating arm that extended about 10 inches perpendicularly from the pole. At the end of the arm was a bronze pin. This pin was used as the rotating axis of a pair of crossed wooden arms. The arms were equal in length, about three feet, crossed perpendicularly at the midpoints, and centered on the bronze pin. Metallic bobs or pondera were suspended by strings from the ends on the crossed arms. The strings were used as plumb lines and were referred to as fila, nerviae, or perpendiculi. Generally, two of the bobs were conical in shape, and two were pear-shaped. Alike bobs were hung directly across from one another. 
The plumb lines of the Groma were used as sights for alignment. The smaller rotating arm displaced the center of the sights away from the pole itself so that the handling of the instrument would not interfere with the alignment. The bobs were usually small and lightweight, and wind was typically a problem. Containers of water were sometimes used to steady the swing of the bobs and it is believed that this is the reason for the use of the pear shaped bobs.
The Dioptra was a more complicated instrument. This instrument sat on a three-footed base and made use of gears and rotating plate screws to rotate the instrument horizontally and vertically. This instrument was usedmainly for leveling, but had a very limited sight distance. 
The Chorobates was an important instrument used for leveling. Vitruvius describes the Chorobates as:
The Chorobates was also constructed so that it could be leveled using water poured into a channel cut into the top of the road. This method was used when high winds made leveling with plumb lines difficult. 
Plumb-bob levels were probably the most common used instruments for leveling. The A-frame level or libella, consisted of a right angle isosceles triangle with a cross bar made of bronze or wood, and a plumb line hung from the apex. When the plumb line coincided with a vertical mark along the cross bar, the two feet were level. The A-frame level could be placed on a straight plank for transferring a level line from one state to another. There is no evidence or writing to the extent of the use of the A-frame level, but due to its simplicity, its use is assumed to be quite extensive. 
The level rods of the Romans were practically the same as and as good as the level rod of today. The rod was approximately 10 cubits long, 5 digits wide, and 3 digits thick. A dovetail was cut along the length of the broadside in which was placed a 10 to 12 digit lead disc mounted to a mating piece of dovetail. The disc was divided into two semi circles one-half black the other half white. The disc was attached to a string that went up and over a pulley on the top of the rod and attached to the back. The disc was raised or lowered using this string. The side of the rod was divided into cubits, palms and digits. As the disc was raised and lowered its height was read from a point along the scaled side. The rod was plumbed using a weight affixed to is side with a string located 3 digits out from the rod, when the string contacted a peg 3 digits in length along the string the rod was plumb. The target circle was sighted down an instrument such as a Chorobates and moved until the white on the bottom of the circle disappeared and the height was read. 
The Groma, the Dioptra and the Chorobates represent some of the essential instruments used by the Romans in their engineering projects. They provided the surveyors with a means of establishing vertical and horizontal alignment. Ropes, rods and pacing supplied the surveyors with methods for measuring distances. Without these tools, the Romans would never have been able to build on such a grand scale.
MONUMENTS OF ROMAN ENGINEERING
The greatness of the Roman Empire was built upon their ability to complete massive engineering projects. The Roman roads and aqueducts stand today as a testament to their engineering capabilities.
Roman roads had four major classifications. First there were public roads (viea publicae), which were paid for by the state. Second, were the military roads (viae militares) paid for by the military. Third, were the local roads (actus), and last were the private roads (privatae). 
Roads were a very important part of Roman culture. They gave the Roman army great maneuverability. Roman roads also improved trade between towns and merchants. Most importantly, they allowed common citizens the ability to move from town-to-town in an easy, compared to the rough trials that were already in existence. 
"All roads lead to Rome." This was true at the time the Roman roads were built. Most roads seemed to head in a straight line towards Rome. There were slight bends in the roads to compensate for alignment errors between cities or other destinations. The roads even went straight around obstacles, such as steep hills or impassable mountains. The roads would angle in straight lines around the obstacles.  If mountain ranges were passable, roads were built through the ranges, and side cut along one side of a mountain. 
Many types of materials were used to make the roads during Roman times. Sand, gravel, slag, cemented crushed stones, and flint stones were typical materials used by the Romans. These materials were not standard for all roads. The materials used to make the roads were drawn from areas near the construction site. As a result, one straight stretch of road may contain three different types of topcoat (road surface) or road base, all depending on the type of materials found in the area. However, if there were not suitable materials within a particular area, acceptable materials were brought in from different areas. 
In order for a road to be constructed, the first thing that needed to be done was to decide where the road was going to go. The path generally was a straight line between two cities.  After deciding where a road was needed, the alignment or path had to be set out, which was dome by a surveyor.
After the alignment was established and adjustments were made, the zone ditch limit was dug. This defined the full limit of the road. A drainage ditch was then dug and this material was used to make the agger (roadbed). The construction would then continue in much the same way as it is done today. 
Roads were made up of three layers. First there was the sub base called the statumen, or the agger. This layer was made of large stones and unearthed material that was dug out of the drainage ditch. The second layer was called the rudus. A mixture of sand or gravel and some clay was used for the second layer. For the top layer, called the metalling, a curb was built first to establish the road width. Then a topcoat material was placed between the curbs. The materials would consist of more gravel, slag (a byproduct of the iron making process) or stones fitted tightly together. 
As the roads were built, a one-foot crown was made so that the road would shed water. In some areas of the road, ruts were purposely built in the top layer to allow carts, wagons, and other vehicles to travel in a straight path. These channels also helped to keep them from sliding off the road in dangerous areas. 
The Roman roads linked Rome to the rest of the Empire. The roads brought in riches from throughout the Empire, but the aqueducts supplied Rome with something more important: life-sustaining water.
TOXINS IN THE TIBER
One of the main reasons that aqueducts were needed in ancient Rome was that the Tiber River was polluted. To begin with, the Tiber River was very dark and silty. Furthermore, throughout the years, Rome's sewer system polluted the river. There was also one more problem; Roman enemies had poisoned the Tiber. Thus, Roman citizens were left with extremely polluted water in the natural water system. The government realized that they needed to solve this problem. Since large numbers of natural springs surrounded Rome, the idea to bring the water from the springs to the city was adopted. 
Eleven major aqueducts were constructed in ancient Rome. These aqueducts brought enormous amounts of water to the city. Some estimates state that the aqueducts could transport around 2570 gallons of water a second, or approximately 222 million gallons a day. However, many believe that the actual amount that the aqueducts were capable of transporting was over twice as much. Large losses in capacity were due to leaking in the aqueducts structures. 
How was the water found? The process was simple really. A worker would lie on the ground just before sunrise, look over the countryside, and look for water vapor coming up over the land. Then they would dig and usually find water near the spot. Another way to find water was to put a bronze bowl in a pit over night. If there was condensation in the bowl the next morning, there was usually groundwater in the spot. 
After water was found, testing was done to make sure that the water was pure. Inhabitants close to the area where the water was found were examined for diseases. Other stipulations were that the water had to be clear, pour well, and boil easily. If water came from a lake there could not be any reeds or wetland areas around it. After the areas passed inspection, the area was considered suitable for use. 
Three different types of water carrying pipes were used in the Roman aqueducts. They were masonry conduits, lead pipes, and earthenware pipes. The most common construction method used involved the use of masonry conduit. There were three different types of masonry conduits. All had stone floors, sides, and roofs. However, there were different formations of the roofs on the conduits. Flat, twin slab, and arc roofs were the different types used in aqueduct construction. All three were constructed with a specus, about three feet wide by six feet tall. The conduits were constructed with a specus so that the aqueducts could be maintained by allowing room to walk within them. 
After the aqueducts were completed, they needed to be maintained. Over time, mineral deposits would build up and reduce water flow. The pipes and supporting structures would also wear out. Things like structure cracks, cracks in the masonry, and leaking cement linings in the specus would occur over time. As a result, aqueducts required a large amount of maintenance. The maintenance was sometimes contracted out, but most of the time the "water commissioner" supervised it. 
Most of the aqueducts were built underground. But when valleys were encountered, the aqueducts were built over them. One system was the inverted siphon system that lay on the valley floors. However, the inverted syphon system was very difficult and expensive to build. The arch bridge system was usually used instead. The arch system would allow the water to flow through a masonry conduit supported by the arch system at a steady grade. 
When the water entered the city, it had to be distributed to its various destinations. Most of the water ran through a cistern that distributed the water throughout the city. It supplied the emperor's palace, private houses, and public structures such as fountains and bathhouses. It could also be stored for a short period in larger cisterns. After the immediate needs were met, excess water was pumped to the sewer system. The wastewater that came from the baths also went to the sewer system. 
The main concern when performing the survey for an aqueduct was leveling. The primary force driving the water from its source to the towns was gravity. Therefore, it was mandatory that the aqueduct be at the proper and precise elevation. There were instances where the gradient from the source to the destination was great enough to overcome errors in leveling, but other aqueducts had a far lesser rate of fall. The leveling instruments and techniques had to be quite accurate.
One concern when trying to recreate and study the surveying of aqueducts is the lack of information. The records for aqueduct construction usually only included the overall fall and length. From this information, the overall grade can be determined, but not for a particular section. The problem is further compounded by the fact that these basic dimensions are not available for all aqueducts. The Roman surveyors used relatively shallow gradients as compared to the steep grades that the Greeks used. 
The first step in surveying a proposed aqueduct was to insure that the water source was actually above the town. Gravity was the primary force moving the water and it was necessary to have a source above the town. Once a suitable site was found, the exact height from the source to the proposed receiving tank was determined. 
The next stage of surveying was determining the actual course of the aqueduct. Due to existing topography and costs, the route taken was not necessarily the shortest. Compromises had to be made concerning the actual route. Minimizing the amount of tunnels or arcades required had to be balanced with maintaining the gradient of the aqueduct so that the water would flow. 
The aqueducts supplied Rome with fresh water, and the roads kept Rome in contact with the rest of the ancient world. Many of these structures remain today.
The Romans built many impressive structures, not the least of which were their roads and aqueducts. These engineering marvels were integral to the survival and success of the Roman Empire. We've seen how they were created, and the important roles that surveyors played in their creation. We've seen the tools and methods used by the surveyors, and the terms, definitions and units that were essential to their everyday practice. The profession of surveying has been a part of civilization for a very long time. The Romans created and experimented with devices and methods of surveying and construction that are a fundamental to these sciences today. The accomplishments of the Roman surveyor stand as a testament to the greatness of their society and their profession.
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