Contributions of Construction Professionals to Archaeology

Introduction

Archaeologists obtain vast amounts of data through the study of monumental architecture. Architecture, and monumental architecture in particular, is often the primary artifact available to archaeologists in their study of the past. Monumental architecture is intended to demonstrate power and/or influence the social order by its scale and iconography.  This type of architecture, including structures such as pyramids, temples, and public buildings form the basis for many inferences by archaeologists concerning population, social structure, and economics of past civilizations. The problem for archaeologists is they do not have the tools or the skills to accurately quantify the labor investment or the possible construction time frame a given structure or site requires.

A structured system of estimating provides archaeologists with the tools to produce reliable, objective, and reproducible methods to quantify the amount of resources committed to the construction of complex ancient architecture. Project scheduling and resource management techniques allow archaeologists to compare multiple what-if scenarios concerning how labor was deployed and how long the construction processes may have taken. Without the application of these practical analytical methods, archaeologists run the risk of describing ancient architecture in subjective terms such as enormous, large-scale, or generations of time. These data offer little quantitative value and could lead to inferences that are misleading or possibly wrong. By using modern construction management tools archaeologists gain better comparative data on which to base and test their hypotheses.

Case Study Background

Civilizations on the north coast of Peru have engaged in building monumental architecture for thousands of years. This area of Peru exhibits a unique geographic niche consisting of a narrow strip of one of the most arid deserts in the world running 350 km. along the coast. It is bordered on the west by the Pacific Ocean and on the east by the Andes Mountains. Prehistoric Andean societies exhibited the ability to muster a labor force capable of building sophisticated engineering and architectural projects. Hundreds of aqueducts, irrigation canals, mounds, pyramids, and compounds represent the tangible remains of these prolific builders.

The city of Chan Chan is located in the Moche Valley on the north coast of Peru and was the capital of the Chimor Empire during the period AD 900 to 1470. With a society based upon divine kingship and nobility, the Chimu dominated the entire north coast until their abrupt end by their defeat and incorporation into the Inca Empire around AD 1400. Through their period of regional dominance and subsequent influence on the Incas, the Chimu played a vital role in the evolution of social complexity in the Andes.

Covering an area of six square kilometers, the urban core of Chan Chan is dominated by 10 monumental adobe enclosures called ciudadelas. The ciudadelas represent the architectural expression of the apex of power. Massive adobe walls rising up to nine meters high and as much as half a kilometer in length surround each compound. They served as the administrative center of the kingdom, the royal palaces of the kings and their immediate families, and with the addition of a burial platform, a mausoleum upon their death. Generally, the ciudadelas are divided into a north, central, and southern sector called the conchone (Figure 1). The north and central sectors each contain numerous plazas, storage buildings, and U-shaped structures called audiencias. Using massive walls, restricted access, and changes in elevation, this purposeful design isolates the elite from commoners, and represents a formal planning tradition that endured hundreds of years. Ciudadela Rivero was best suited for analysis from a construction perspective due to its extensive mapping and existing research.

The interpretation of the architecture at Chan Chan contributes significantly to theories of the social, political, and economic structure of the Chimu. The monumental size of the ciudadelas implies the control of labor, the spatial layout suggests differences in rank, and the large proportion of space allocated to storage infers centralized control of a redistributive economy. However, there are no reliable estimates of how much labor was involved in constructing a ciudadela, how long it may have taken to build, and what degree of control and coordination was actually required. These data are directly relevant to theories concerning the sociopolitical organization of the Chimu.

Methodology and Data Collection

Overview

This retrospective approach to the construction process, and integration of the design, estimating, and scheduling functions, produces a powerful means of quantitative analysis. The design defines what to build, the estimate represents its labor cost, and the schedule simulates the construction strategy and labor distribution, and calculates the project’s duration. This investigation took the point of view of the contractor operating within the social structure and technology available during the construction of the ciudadelas at Chan Chan. The subsequent discussion describes the use of contemporary project management tools and techniques in the context of constructing Ciudadela Rivero.

The process of quantifying the labor investment in a project required:

1.        Defining the Scope of Work, and developing a Work Breakdown Structure.

2.        Performing a Quantity Survey to determine the types and amounts of installed materials. 

3.        Identifying and estimating productivity in the form of unit rates.

4.        Calculating the Project Estimate from the installed quantities and unit rates.

Estimating the overall duration of a project involved:

1.        Preparing Logic Diagrams to represent the project work plan(s).

2.        Establishing crew sizes and activity durations.

3.        Calculating a CPM schedule based on the logic and resource requirements.

4.        Comparing target schedules to quantify differences in work plans.

5.        Performing risk analysis to account for uncertainty.

Scope of Work

A Scope of Work (SOW) was defined to identify all activities required to construct the project based upon the plans and specifications. The Work Breakdown Structure (WBS), based upon the scope of work, divided the project into increasingly detailed levels culminating in discrete tasks involving differing time and labor requirements (Figure 2).

Aided by plan maps and a detailed architectural survey of the compound, field research revealed that while the compound was in ruins, there were ample examples of nearly intact masonry to reasonably estimate the sizes of the original structures. In many cases wall abutments and remodeling efforts indicated probable construction sequences. The conclusion was that the existing layout of Ciudadela Rivero is the result of at least two major construction episodes, and that originally, only a single tapia (rammed earth) wall surrounded the ciudadela. It is possible and even probable that remodeling occurred in other areas of the compound. Specifically included in the scope of work for the original configuration is the general excavation at the site and the procurement, manufacturing, transportation, and installation of all materials in all structures within and including the massive tapia walls.

Labor Quantification (Estimating)

In terms of cost, the only meaningful measure is labor hours. An accurate measure of the labor investment in a structure is useful to archaeologists since it serves as a basis of comparison between structures on a relative basis.

The development of productivity rates began with an analysis of the structures, tools, construction methods, and techniques available at the time of initial construction. Where there was a close match, contemporary productivity information from published construction estimating standards were used as a starting point and adjusted as required to fit the context of the times. Experimental data existed from previous research done by others (Abrams 1994, Erasmus 1965), and conceptual estimating providing labor rates for a few activities when no other points of reference existed. Combining these productivity rates with the material quantities yielded the total labor requirement for each activity. Summarizing the labor requirements of the activities up the WBS hierarchy generated the total project estimate.

Building an adobe wall is an example of unit rate development. Construction of adobe walls uses simple, time-tested techniques that emphasize quantity over quality, strength over skill. Few of the tasks involved using skilled labor and workers were essentially interchangeable throughout. Most walls at Ciudadela Rivero alternate courses in a runner-header bond with mortar applied to only the top surface of the courses. The curing rate of the adobes and the mortar limit the production of two to three courses per day.

Since adobe construction remains essentially unchanged from the time of the Chimu, contemporary sources provided a good starting point. One published standard (R.S. Means 1999:134) estimates placement of 555 adobes (35 cm x 10 cm x 25 cm) by a 5-person crew, in eight hours, while Wilson (pers. com.) experiences a rate of 500 adobes with a 3-person crew (Figure 3). In order to accommodate varying brick sizes, the number of bricks are converted into their equivalent volumes to yield a reasonably accurate measurement of productivity across the range of brick sizes. However, each estimate assumes the use of a wheelbarrow, a convenient water source, and a machine mixer for mortar. Since the Chimu employed only manual methods, the addition of two workers to each crew adjusts the rates to take into account manual transportation and mixing of materials, which is consistent with anecdotal data from informants in Peru gathered by the author. The resulting data from all sources are relatively consistent and form the upper and lower limit of the productivity range. The most likely rate of 10 hours per cubic meter of wall is the average, with an optimum crew of 4 to 6 workers, depending on the size of the wall.

Based upon the most likely productivity rates, the project estimate for the construction of Ciudadela Rivero in its original configuration is 2.1 million labor hours with an 85% to 95% confidence factor as quantified through Monte Carlo simulations.

Monte Carlo (Primavera 1996) enables modeling the effects of uncertainty by calculating project data many times with different input values that represent all possible scenarios in a situation.  The results show the logical consequences of a specific set of risk assumptions, including duration or estimates. By allowing for a range of possible productivity rates for each activity the simulation produces output that includes a probability distribution for the estimate of the project.

Scheduling

Quantifying the labor expenditure for the construction of Ciudadela Rivero provides useful data for comparison purposes. However, archaeologists are also interested in the societal implications involved in utilizing these resources and their desire to explore its meaning necessitates the consideration of time and the dynamics of construction. Integrating the project estimate into a resource loaded Critical Path Method (CPM) project schedule permitted modeling theories of labor organization by observing the effects on resource utilization under multiple construction scenarios, and calculating overall project durations. This application of CPM presented a versatile tool to dynamically model, within reasonable parameters, how resources might have been used within the context of prehistoric construction.

A project schedule is the representation of a specific construction work plan concerning the sequencing of work and the deployment of resources. Factors influencing the overall construction plan include the site layout, availability of raw materials, water, and housing. Development of the schedule involved determining the skill levels required in terms of crafts, optimum crew size, duration, and the logical relationships between activities. Procedurally, each activity was evaluated in terms of optimum crew sizes and productivity to determine the total resource requirements and duration. Fragnets were developed to represent the construction of the numerous individual structures that make up the compound, then arranged to reflect possible overall construction sequences. An important source of construction sequencing is identifiable in the architecture itself where items such as wall abutments and structural connections reveal clues to their internal chronologies and phases. Other criteria affecting the order of construction sequences include the knowledge of the construction techniques and methods used, local building traditions, and labor availability.

An optimum or unrestricted schedule was developed with no restrictions on resources and maximum flexibility as to construction sequencing and stored as a target schedule to represent a baseline for comparison purposes. Subsequently, multiple what-if scenarios were generated using various combinations of labor organization theories and construction sequencing options and compared to the baseline and each other to illustrate the effects of each scenario on resource and time requirements.

The unrestricted schedule representing the quickest practical completion of the ciudadela assumes unlimited resources available on an as-needed basis. Based on the most likely durations the estimated completion time was 61 calendar months. In general, the average peak labor requirements range from between 200 and 280 workers, with a peak of 400. The requirement to call upon and release large numbers of workers on a daily basis makes this schedule theoretically possible, but not necessarily practical. Figure 4 illustrates and compares overall durations.

Beyond the normal project constraints are sets of relationships resulting from labor allocation strategies that exert a significant influence on the construction strategy. Manipulating these organizational relationships is an important means of simulating realistic building scenarios and comparing theories. For example, there is general agreement that a labor tax was in place at Chan Chan. Since societies did not use money or any standardized currency, the state extracted revenue from the population in the form of labor. This form of taxation is based upon kin groups or villages, and was most likely operational during the construction of Chan Chan (Moseley 1975). There are two approaches applicable to allocating labor under a labor tax system, the work party and the task specialization and differentiation models.

In the work party theory, workers within the same social group were responsible for a specified quantity of completed work such as a storeroom. This requires each group to perform a series of identical repetitive tasks i.e., making bricks, hauling them to the site, and setting them in place. This creates serial construction sequences that generally extend the length of the schedule (Figure 5). Construction coordination and control tends to stay more within the group. Based on the most likely durations the estimated completion time was 73 calendar months with the average peak labor requirement of 200 – 250 workers.

Others suggest this theory is not universal, that task specialization and differentiation better describes labor organization at some sites. Under this model, each group of workers is responsible for a given task or tasks, such as making and transporting adobes, with a separate group responsible for erecting a wall. This is most efficient when multiple groups of workers perform their tasks so construction activities proceed in parallel. In this case each group depends upon other groups to perform their tasks in a timely manner. Consequently, coordination of the construction is required between groups requiring high-level supervision. In addition, groups can complete activities in advance such as adobe making that creates some flexibility in scheduling. Task specialization also tends to exhibit more potential for productivity improvements due to the learning curve. The schedule representing the task specialization model uses the same logic as the unrestricted schedule. Limiting the overall number of workers and utilizing float smoothed the major peaks in labor to allow for a more balanced workforce. Based on the most likely durations the estimated completion time was 67 calendar months with the average peak labor requirement of 200 – 280 workers.

Probabilistic Scheduling (Risk Analysis)

As shown thus far, CPM scheduling is deterministic and uses a single estimate and duration derived from what is best described as the most likely unit rates. This approach presumes there is no uncertainty in productivity and does not account for any variability. Since it is impossible to make precise estimates for prehistoric construction, the most likely unit rates were bracketed by optimistic and pessimistic rates representing a range of values, and thus, a higher level of confidence. The result is that the effect of this uncertainty on the project estimate and schedule is quantifiable in terms of probabilities.

Monte Carlo simulations were run to generate numerous project outcomes based upon the full range of productivity rates. Frequency distribution histograms and cumulative probability curves plotted the results. These simulations indicated that the unlimited resource, task specialization, and work party models had only a 30 % probability of finishing within the deterministically derived end date calculated from the most likely durations. Using the 95% probability range, the length of each project was 64, 70, and 77 months respectively.

Impact on Archaeological Theory

Mass Labor, Scale of Construction, and Social Complexity

Archaeological theories relating to economic impact and strong centralized governmental control were based upon the assumption that building a ciudadela took massive amounts of labor generations to build  (Schwartz 1982: x). However, as demonstrated here, a workforce of roughly 250 persons could have constructed Ciudadela Rivero in approximately 6 years, representing about 2.1 million labor hours.

While substantial in size and scale, the labor requirements are modest, especially since an estimated 30,000 persons inhabited Chan Chan during its final phase. The maximum number of workers required under the most aggressive schedule (unrestricted) was only 400, and then for just a few months. Even doubling the labor force to an average of 500 workers in an attempt to crash the schedule to its shortest possible duration represents a relatively minor part of the population dedicated to construction.

One of the foundations of ancient Andean societies was the ability to mobilize large work forces to construct monumental architecture. While more labor intensive efforts are evident in other structures in the Moche Valley, it is difficult to extend the concept of controlling massive workforces to the construction of the ciudadelas at Chan Chan. The amount of time and labor invested in the ciudadelas is much less than previously thought. In light of this research, theories concerning the control of mass labor and social complexity based solely on the monumental architecture of Chan Chan need revisiting.

Local vs. Imported Labor

There does not appear to be the need to import workers from surrounding areas, since redirecting a small portion of the resident population to constructing a single ciudadela seems entirely feasible. Due to the manageable size of the workforce, it is possible that the residents of Chan Chan bore the tax levied to construct the ciudadelas while the rural population met their obligations at or near their own region. Rotating groups from within the resident population gives the builders considerably more control and flexibility than coordinating, feeding, and housing workers from distant communities. Additionally, relying upon the non-agricultural resident workers has the advantage of eliminating the seasonal availability of workers. If workers living outside of Chan Chan performed the construction, the decision to use outside labor rather than the resident population was one of choice not necessity.

Split Inheritance

The split inheritance or one king/one compound theory posits that the major compounds of Chan Chan were the palaces of the kings of Chimor. Each ruler built one such structure to house himself, be the seat of government, and serve as the center for the management of his wealth. In accordance with a law of split inheritance the palace passed to the king's corporation of secondary heirs after his death. His principal heir became the next king and built a new palace.

To satisfy this theory, the construction of the new palace must be rapid to the point of being achievable in a timeframe well within the lifetime of a king. The estimated six-year construction time for Ciudadela Rivero easily fits within this time parameter. However, Ciudadela Rivero is the smallest of all the compounds, while Gran Chimu, the largest compound is more than twice its size. Scaling up the labor requirements and construction time indicates that Gran Chimu required 500 workers accumulating over 6 million labor hours over a nine-year timeframe; still within the required parameters for the 1 king/1 compound theory. The concept of split inheritance is easily feasible in terms of the relatively short construction time.

Dual Rule

Some researchers hold that at Chan Chan, the theory of dual rule suggests that rather than sequentially, the last four ciudadelas were built concurrently as pairs or even simultaneously (Cavallaro 1988, Netherly 1990: 483). Others disagree stating that the rapid construction of the last four ciudadelas is unfeasible without a major shift in the economy of the kingdom (Mackey & Klymyshyn 1981: 104; Mackey 1987: 127).

The last four compounds built were Velarde, Bandelier, Tschudi, and Rivero. Factoring the data for Rivero yields that constructing Velarde and Bandelier as a pair required an average workforce of approximately 600 workers in 8.3 years. While at Tschudi and Rivero 500 workers could complete the compounds in 8.5 years. The data indicates that 1100 workers could accomplish building all four compounds simultaneously in 8.5 years accounting for almost 12 million labor hours.

Therefore, while building the last four compounds simultaneously requires more than a four-fold increase in labor over constructing Ciudadela Rivero alone, it is still within reasonable limits given the local population. In terms of labor requirements and construction times, these data suggest that dual or quadripartitioning was feasible and even the most aggressive building program, represented by the simultaneous construction of the last four compounds, does not have enough impact to cause any major shifts in the local economy. Therefore, theories of dual or quadripartite rule, requiring the simultaneous construction of two to four compounds, cannot be eliminated based upon construction requirements.

Significance of Research

This article serves to demonstrate the applicability of construction project management practices to the field of archaeology. By using this retrospective approach, project management professionals can contribute to the body of archaeological knowledge on issues concerning scale of construction, organization of labor, and ultimately, the complexity of ancient social organizations. The methods and processes presented here refine and extend the use of construction industry estimating standards to provide accurate, systematic, and reproducible estimates of labor costs on large-scale complex ancient architecture. By introducing the concepts of construction scheduling, archaeologists have a tool that can dynamically simulate the construction process using numerous what-if scenarios to estimate construction times of ancient architecture under various theories.

References

The author performed all construction research presented in this paper. The references listed below provide background from the archaeological perspective.

Abrams, E. M. (1994). How the Maya built their world; energetics and ancient architecture. Austin: University of Texas Press

Cavallaro, R (1988) Architectural analysis and dual organization in the Andes. Ph.D. dissertation, Harvard University, Cambridge.

Day, K. (1973) The Architecture of Ciudadela Rivero, Chan Chan, Peru. Ph.D. dissertation, Harvard University, Cambridge.

Erasmus, C. J. (1965)            Monument Building: Some Field Experiments. Southwestern Journal of Anthropology, Vol. 21, No. 4

Mackey, C. J. (1987) Chimu administration in the provinces.  The Origins and Development of the Andean State, edited by J. Haas, S. Pozorski, and T. Pozorski, Cambridge Cambridge University Press 121-144

Mackey, C. J. & Klymyshyn, U (1981) Construction and Labor Organization in the Chimu Empire.  Nawpa Pacha, (19), 99-109

Mackey, C.J. & Moseley, M (1974) Twenty-Four Architectural Plans of Chan Chan, Peru. Cambridge: Peabody Museum Press

Means, R. S. (1999) Open shop building construction cost data. Kingston, R.S. Means Co. 134

Moseley, M. (1975) Prehistoric principles of labor organization in the Moche Valley, Peru. American Antiquity, 40 (2) 191-196

Netherly, Patricia J. (1990) Out of Many, One: The Organization of Rule in the North Coast Polities. The Northern Dynasties: Kingship and Statecraft in Chimor, edited by Moseley & Cordy Collins. Washington, D.C.: Dumbarton Oaks Research Library and Collection 461-485

Primavera Project Planner, (1996) Version 2.0.  Primavera Systems, Inc. Bala Cynwyd, PA

Rowe, John Howland (1948) The Kingdom of Chimor. Acta Americana,. 6. (1-2) 26-59

Schwartz, Douglas W. (1982)             Foreward. Chan Chan: Andean Desert City, edited by Moseley & Day. Albuquerque: University of New Mexico Press

Wilson, Quentin : Instructor of Adobe Construction, Northern New Mexico Community College