Background

Roman Engineers (Architects)

Classical Roman architecture grew from Greek architectural developments and flourished during the Roman Republic and Empire. This is especially evident with countless architectural feats still preserved and present today, ranging from the universally famous and iconic Colosseum, Pantheon and aqueducts to the lesser known and more common structures for everyday public use such as bridges, roads and houses. As suggested by the Greek etymology of the word “architect” (arkhi-, “chief” + tekton, “builder”), a Roman architect at the time had an impressive repertoire and possessed a variety of skills. This included engineering, urban planning, designing, contracting, supervising, etc., all considered to be completely separate fields today in modern times. The wide variety of topics covered by Vitruvius in De Architectura in relation to architecture (later discussed) is a reflection of the range of knowledge and skills required for the position of an architect at the time. Architects were in charge of basically all aspects of a construction of a building or structure, thus needed to be educated in a variety of subjects. According to Vitruvius, an architect should be knowledgeable in a range of subjects that included geometry, history, philosophy, music, theatre, medicine and astronomy, in order to fully take in his surroundings and construct a successful structure. He stated, “The architect should be equipped with knowledge of many branches of study and varied kinds of learning, for it is by his judgment that all work done by the other arts is put to test.”

Vitruvius and De Architectura

Arguably the most famous architect of the time was Vitruvius, due to his treatise on architecture, De Architectura libri decem (Ten Books on Architecture). Born Marcus Vitruvius Pollio around 80-70 BCE and raised and educated in Campania or Rome, Italy, little is actually known about the personal life of the celebrated ancient architect and writer. Bits and pieces are gained from his manuscripts alone. Vitruvius was a freeborn Roman citizen but not necessarily of high (equestrian) class. He had a broad “liberal arts” education, which is evident in his writings. It is presumed that after his liberal arts education, he was apprenticed to an architect, if not several architectural teachers. Vitruvius’ actual career may have started while he was in his thirties, which would have been around 50 BCE, about the time of the outbreak of the second Roman civil war between Julius Caesar and Pompey (49 BCE). The next two decades of his life were likely spent in military campaigns, initially working as a Caesarian staff architect. It is also suggested that he was on Caesar’s military campaign, as well. According to the Unitarian minister, author and compiler of reference works, Rev. John Platts in his first volume of A New Universal Biography, Vitruvius was “greatly esteemed by Julius Caesar.” After the murder of Caesar, he continued his work in military campaigns under the reign of Augustus in a variety of locations including Northern Italy (Gallia Cisalpina), the Adriatic Coast (Fano), the Alps (Larignum), Marseilles, North Africa and Greece. His work included war machines, public buildings and aqueducts. During Vitruvius’ later career, he was patronized by Augustus. Ingrid D. Rowland and Thomas Noble Howe, translator and commentator in Vitruvius: Ten Books on Architecture describes this patronage as Vitruvius receiving a “commoda” from Augustus, a sort of regular annuity that would allow him the leisure to study and write. De Architectura was either a product of this patronage or what allowed Vitruvius to receive sponsorship from Augustus.

Figure 1. 1684 depiction of Vitruvius presenting De Architectura to Augustus (Source: Vitruvius on Architecture by Thomas Gordon Smith)

De Architectura libra decem is a compilation of previous knowledge as well as a reflection of Vitruvius’ own knowledge and understanding of architecture and engineering. Written sometime around 15 BCE, the treatise was written for and dedicated to Augustus after his win over Mark Antony and Cleopatra in the Battle of Actium (31 BCE) which lead to his rise in power and solidified his status as the first Roman Emperor. De Architectura was meant to be a guide for Augustus on building projects. Vitruvius made his dedication in the preface of Book I, for the benefit of Augustus’ education and construction projects. Augustus (63 BCE – 14 AD), was the founder and thus, first Emperor of the Roman Empire. Notably famous for bringing peace to the Roman Empire and radically changing the Roman landscape through numerous building projects. Augustus himself more specifically lists his accomplishments in the //Res// //gestae divi Augusti// (The Deeds of the Divine Augustus) and famously said, “I found Rome a city of bricks and left it a city of marble.” The reign of Augustus brought a revival in Roman architecture and construction. He began a trend of constructing buildings for the public as an emperor’s display and sharing of the wealth, success and strength of the Roman Empire. Vitruvius addressed this and mentioned in his preface to Book I of De Architectura that his writing of the treatise was a means to aide Augustus in serving the public: “But when I saw that you were giving you attention not only to the welfare of society in general and to the establishment of public order, but also to the providing of public buildings intended for utilitarian purposes, so that not only should the State have been enriched with provinces by your means, but that the greatness of its power might likewise be attended with distinguished authority in its public buildings, I thought that I ought to take the first opportunity to lay before you my writings on this theme.”

As stated in its title, the treatise is divided into ten sections or “books”, each covering different aspects of architecture and city planning. The different books are broken down and categorized into:

1. City planning, general architectural/civil engineering, and required education of an architect
2. Origin of dwelling, site selection and building materials
3. Theory, modes of design of temples and order of architecture
4. Continuation of Book III; more on Ionic, Doric Corinthian and Tuscan order and temples
5. Various types of civic buildings (forums)
6. Domestic buildings in town and country
7. Finishes: floors, vaults, stucco and painting
8. Water detection, quality, supplies, storage and transportation
9. Sciences influencing architecture/civil engineering: astronomy, astrology, clocks and sundials
10. Construction and use of military engines, mechanical and surveying devices

The treatise has been essential to archaeologists and architectural historians in interpreting remaining physical evidence and literary descriptions of temples and other buildings/structures. Besides its original illustrations, it is the only surviving contemporary source on classical architecture and provides us a window into the times of the Roman Empire. More specifically, Vitruvius’ writings also influenced the Renaissance definition of beauty in architecture, with the revival of Classical Rome.

Book III

Book III of De Architectura begins with the derivation of the perfect numbers in relation to each other and circle and square shapes, which Vitruvius uses to determine ideal symmetry and proportions. Ideal human body proportions are derived and used as a scale for measurements; this same idea is also later used for temples. Vitruvius then classifies temples by the arrangement of the colonnades:

1. temple in antis
2. prostyle
3. amphiprostyle
4. perpteral
5. pseudodipteral
6. dipteral
7. hypaethral

Figure 2. Illustration showing the classes of temples according to arrangement of colonnades (Source: Hellenica World)

Temples are then classified into five different styles, based on the determination of the shaft height of the columns and intercolumniation:

1. pcynostyle: “close-set columns”
2. systyle: “slightly more ample intercolumnar space”
3. diastyle: “even more widely spaced”
4. araeostyle: “columns stand further apart than is desirable”
5. eustyle: “placement is right”

Figure 3. Illustration showing classification of temples according to intercolumniation, taken from (Source: Hellenica World)

Vitruvius continues with listing rules for the dimensions and heights of columns depending on their class as well as column proportions. At the end of this section on columns within Book III, a standout quote from Vitruvius is: “For the eye is always in search of beauty, and if we do not gratify its desire for pleasure by a proportionate enlargement in these measures, and this make compensation for ocular deception, a clumsy and awkward appearance will be presented to the beholder.” This tells us that the use of columns in temples play more of a decorative role rather than a functional one as load-bearing structures. The use and size of columns can be a reflection of the wealth and success of the Roman Empire at this time.

The rest of the book finished off with rules on the construction of the foundation and various substructures of temples, along with beginning an in depth discussion of proportions of the base, capitals and entablature of columns of the Ionic order.

Book IV

Book IV of De Architectura picks up where Book III left off by continuing the discussion of the Corinthian and Doric order of columns. He begins with the origin and invention of the three orders and continues with more rules of proportions for Corinthian capitals, as it was explained that the capitals were the only difference between Ionic and Corinthian columns, and Doric temples. Vitruvius also discusses principles for proportions of the cella and pronaos (portico) of the temples and its doorways. Book IV ends with smaller discussions on Tuscan temples, circular temples and altars in general.

Books III and IV had a large emphasis on the idea of proportions. Vitruvius states that these rules based on proportions were fundamental in protecting against structural failure, along with creating an aesthetic that pleases the eye. Vitruvius has also remained true to his initial agenda of aiding Augustus in designing and constructing these buildings for the people. For example, in the chapter on the proportions of intercolumniations and of columns, Vitruvius mentioned, “For the idea of the pteroma and the arrangement of the columns round a temple were devised in order that the intercolumniations might give the imposing effect of high relief; and also, in case a multitude of people should be caught in a heavy shower and detained, that they might have in the temple and round the cella a wide free space in which to wait.”

Structure of Columns

It is evident from De Architectura that Roman architects of the time relied on correct and specific proportions and ratios in order to construct a structurally sound building. Although Vitruvius also mentioned foundations and materials, he held a heavy discussion of columns and proportions. As previously stated, Vitruvius found them impertinent in ensuring a structure would not fail. Thus, a very simple modern engineering introduction to columns will be needed to examine the qualifications needed for a column to succeed and how a column could fail. This could also be used as a general comparison to the rules of proportions in De Architectura to understand why these rules for the construction of temples, which were essentially just geometry in combination with observations from hundreds of years of trial and error, worked applying the modern knowledge of engineering and physics we have today.

A column, in engineering terms, is vertical structural element that, through compression, carries the weight of the structure above, through the column itself, and to the other structural elements below. Columns are compression members subject to axial forces. There are three types of columns based on type of failure modes: short columns, long or slender columns and intermediate columns.

Failure Modes

Failure in short columns occur when the direct stresses are dominant and crushing of the material occurs.

Figure 4a

For a long column, failure occurs by lateral buckling. The buckling occurs before the normal stress reaches the strength of the column material. Buckling occurs when the load exceeds the axial strength of the column and causes it to deform. It originates at the weakest point in the column, which can either be at a point furthest from the supports or at a point where the material has anomalous, or abnormal, microstructure. The stress and strain at the point of deformation will spread until it exceeds the tensile, compressive or shear strength of the material. In other words, buckling occurs when the load applied is greater than the critical load of the column,or the maximum force that it can withstand. Buckling is an important concept as it is one of the major causes of failures in structures. A simple example to explain what buckling looks like would be the effect of when one pushes the ends of a bookmark together.

Figure 4b

Failure in intermediate columns is a sort of combination of both failure in short and long columns. Failure occurs in both lateral buckling and crushing of the material.

Figure 4c

Figures 4a-4c, (Source: efunda)

Buckling and Euler’s Formula

The Swiss mathematician and physicist Leonhard Euler (1707-1783) determined a formula that predicts the critical buckling load for a straight pinned end column, otherwise known as the ideal column:


where,

• P = critical load on the column
• E = Young’s modulus of the column material (measure of the stiffness of a solid material)
• I = moment of inertia of cross-section
• K = effective length factor, a dimensionless coefficient determined by the conditions of the end support of columns (can be assumed to be 1 for columns with hinged ends and the sake of simplicity)
• L = unsupported length of the column
• KL = effective length of the column

An ideal, or perfect column is long, straight, homogenous and is subjected to concentric compressive axial loads. From this formula, it can be noted that the critical buckling load decreases as the length of the column increases and is dependent on Young’s modulus of the material and dimensions. Once the column reaches the critical load, it will buckle.

Critical Stress and Slenderness Ratio

The critical compressive stress is the stress corresponding to the critical load of the column. The formula for the critical stress is obtained by dividing the critical load by A, the cross-sectional area of the column:

sigma = P/A (or F/A as in Figure 5)
The effective slenderness ratio is the ratio of the effective length of the column (KL) to the least radius of gyration of its cross-section (r). It is a measure of the column’s flexibility. Its formula is given by: . The slenderness ratio can also be used to determine the type of column and when Euler’s formula is valid. A short column will have a low slenderness ratio and thus, will crush before it buckles. A large slenderness ratio (long column) will yield a smaller critical load and thus, govern the design strength of the column.

Figure 5. Simple graph displaying relationship between critical load and slenderness ratio (Source: efunda)

Temple of Divus Julius