12 Methods of Excavations : Introduction, Trial, Vertical Excavation and Step Trenches

V. Selvakumar

 

1. Introduction

 

Archaeological excavation is a systematic process of digging of natural and cultural layers, whichhave geological deposits, ecofacts, material culture and their multiple contexts and built environments, to document and recover the material remains and data onmultifarious contexts in order to understand the past human behaviour and the cultures on the whole. Archaeological excavation is often referred to as a documented destruction. The archaeological excavations can be undertaken on land, underwater and marshy environments, and the methods and techniques would vary according to the context of the excavation.Normally, the soil layers are slowly scraped or dug gently depending upon the context and the removed sediments are sieved to recover the artifacts, evidencesand samples for various analyses for the interpretation of human behaviour.

 

What is a method? Method is a procedure to undertake an operation or expedition. Method may include a number of processes, steps and techniques to achieve an objective. Sometimes, the terms methods and techniques are used interchangeably. Method is “a process by which a task is completed; a way of doing something” and technique is “the practical aspects of a given art, occupation etc.; formal requirements” (http://wikidiff.com/method/technique).

 

The methods and techniques related to excavation,generally,involve layout of trenches, understanding, removal and documentation of the layers or cultural deposits, contexts and relationships (stratigraphy), cultural materials and all kinds of possible evidences and their analyses for a proper interpretation of human cultural behaviour. There are at least two dimensions in any archaeological site, or what we call as space and time in history, and the horizontal and vertical methods of excavations cover these two components.Conventionally, the mode oflayingout of the trenches and the nature of the excavation are classified as method of excavations.However, more than the horizontal and vertical methods that are often discussed in the textbooks, the actual processes and techniques of excavations and documentations are important. The techniques of excavation for both these horizontal and vertical approaches are identical, and the evidencesare documented and recovered carefully, in both these methods.

 

Based on the layout of trenches, area of excavations and the objectives, the excavation methods are broadly categorized into vertical and horizontal methods.In this module, besides the introduction to the methods of excavations, we will look into the advantages, and disadvantages of trial, vertical and step trench methods of excavations. The techniques of excavations are covered in other modules.

 

The job of excavation does not stop with the excavation itself. Analysis of stratigraphy, context and material remains are important at the post-excavation stage to understand the cultural remains that have been excavated and to prepare the report of the excavations. Therefore, when we talk about excavation, we are dealing with the entire process of research right from the problem formation to the publication of report and conservation and recovery of the excavated materials through museum display and archiving of excavated materials.

 

The process of excavation in India is regulated by the Archaeological Survey of India and the excavation in the country is governed by the Ancient Monuments and archaeological Sites and Remains act of 1958 and the associated amendments and the recent AMSR Act 2010.Archaeological excavation requires permission from the Archaeological Survey of India and the report of the excavations along with the antiquities recovered has to be submitted after the excavations. Only trained archaeologists are given permission for excavation. The applications for excavations are processed by the Central Advisory Board on Archaeology (CABA).

 

2. History of Excavation Methods

 

Archaeological excavation techniques were mainly developed in the 19th and 20th centuries. The excavations that were conducted before the 19th century were not generally systematic and in a sense archaeology developed as discipline only from the 19th century. The antiquarians were mainly interested in collecting attractive artifacts without much bothering about the culture and the people behind the antiquities.Giovanni Battista Belzoni was an antiquarian, who worked in Egypt,andhe is often criticized for the lack of methods in excavation. The third American president Thomas Jefferson is considered to have undertaken systematic excavations as early as 1781-82. He excavated native Indian remains near Blue Ridge Mountains, close to Monticello estate in the vicinity of the Rivanna River, north of Charlottesville in Albemarle County in Virginia (USA). General Pitt Rivers and Flinders Petrie and Robert Eric Mortimer Wheeler, Kathleen Kenyon, Leonard Woolley, Jens Jacob AsmussenWorsaae,are some of the scholars who contributed to the improvement of excavation methods. Professional excavators developed mainly in the twentieth century.Philip Barker and Edward Harris are among the important excavators who have contributed to the development of excavation methods.

 

The excavations by various scholars such as James Babington, Meadows Taylor, Alexander Rea were important attempts in the 19th century. Sir John Marshall, R.D. Banerjee and DayaramSahmi made noteworthy contributions to the excavations in India in the early twentieth century.

 

Robert Eric Mortimer Wheeler can be considered a pioneer in the development of proper archaeological excavation methods in India. He organized the Taxila School of Archaeology in which many Indian archaeologists were trained. H.D. Sankalia, B.K. Thapar and several great personalities from the Archaeological Survey of India, Deccan College and other Indian Universities contributed to the archaeological excavations in India.Subsequently, the collaboration of Indian and Western archaeologist have led to the introduction of new methods of excavations and recording in the archaeological excavations of India.

 

2.1 Tools and Implements

 

For undertaking an archaeological excavation,several tools and implements are required. A few of the important tools and implements and their functions are listed below and a detailed list can be found in the Appendix 1 at the end of this Module.Trowels and knives are used for scraping, removing the soil layers and for exposing artifacts, features and architecture during an excavation. While trowels are used in many excavations across the world, knives are also used by researchers. Small pickaxes are used gently for excavations in some contexts. The nature of the soil deposit is a factor determining the use of specific tools. Sandy deposits can be easily excavated with a trowel or knife, for a hard clay deposit pick axe has to be used.

 

Shovels, dustpans, buckets, and baskets are required for removing soil from the site of excavation and transport them to the site where the sieve is located. Sieve is another important tool required for recovering artifacts from the excavated soil.Brushes of various sizes and hardness are required to clean the excavated surface for observing the features underneath, and also for cleaning the excavated area for photography.Tape measures are essential for measuringand preparing drawings of the various components, features and architecture of a trench.Section trimmers and root cutters are important for clearing the section of the trench and dissection tools are necessary to excavate delicate features such as burials, skeletons or other features. Photography and survey and documentation tools are neededto document the data collected in the excavations.

 

2.2 Human Resource

 

Excavation is a team work and it cannot be done by just one individual. Human resource is very important for an archaeological excavation. There is no strict rule for the number of persons and professionals to be involved in an archaeological excavation, and depending upon the funding and resources available, several specialists are involved. In a small excavation, the director may perform the task of photography and documentation. Normally,an archaeological project will have a director or principal investigator. This person is the backbone of the project and is responsible for planning, designing and organising and conducting the research. Sometimes, excavation alone can be a research project or excavation can be part of a research project covering regional surveys.The project may have co-investigators or co-directors if it involves team work. Site supervisors may be required depending upon the size of the excavations. Trench supervisors are important for an excavation, since each trench can be better managed by the trench supervisor who can supervise the digging and documentation processes, and make observations on the finds, contexts and relationships. Skilled excavators (archaeologists and labourers) andstudents/researchers or workers are important for undertaking the actual task of excavation and for collecting the artifacts carefully. Surveyors/draughtspersons are necessary for preparing the map of the site and the excavated features. Antiquity registrars are necessary to document the antiquities in a register, since it is a legal requirement under the law of India to send the report on antiquities to the Archaeological Survey of India. The various material remains would require specialists for studying ceramics, beads, human and animal bones and soils.Some of the specialists may be involved in the post-excavation stage; but involving them in an early stage is a better option.

 

3. Excavation Methods and Techniques

 

There are at least two dimensions in any archaeological site, as space and time components in history. The horizontal and vertical methods cover these two components. The nature of the excavation is related to the objectives of the research, and the techniques of excavation for both the horizontal and vertical approaches are identical. The evidence has to be documented and recovered carefully from the excavated sediments. The excavation proceeds gradually, and locus (context) or activity areas are marked and they are excavated. Locusmeans space and refers to a context excavated in a trench and some archaeologists use locus-based method. Harris Matrixis used to convey the relationships among the loci.

 

3.1 Excavation and its implications

 

Excavation does not stop with the digging itself and digging is the beginning of an excavation. Analysis of stratigraphy, context, relationships of loci through Harris Matrix and material remains are important at the post-excavation stage to prepare the report of the excavations and to understand the cultural remains that have been excavated. It deals with the entire process of research right from the problem formation to the publication of report. Conservation and recovery of the excavated materials through museum/site museum display and archiving of artifacts, samples and materials are also important aspects of the excavation process; mainly in the contemporary context, where heritage management is given more attention.

 

3.2 Research Problem

 

Research problem is an important component of an archaeological excavation. Often the most excavations are done just to know the cultural sequence and chronology. Even then,cultural history could be considered as a main research problem. However, with the regional approaches gaining ground, the excavations nowadays seek to understand the cultural context, behavioural patterns and landscape archaeological perspectives. Some of the excavations proceed with more complex research problems and hypotheses. The research problem varies depending upon the context and local condition and previous research undertaken in the concerned area.The research problem determines why a particular method of excavation is chosen. Research design refers to the strategies adopted to address the research problem efficiently.Carefully, constructed research design would help resolve the research problems.

 

4. Methods of Excavations

 

Based on the objective, layout and extent and nature and approach, the excavation methods may be classifiedinto:

  • Augur or Coring Method
  • Trial Excavation Method
  • Vertical Method
  • Step TrenchMethod
  • Horizontal Method
  • Quadrant Method
  • Open Area Method

 

Among these methods,coring and trial methods are more particularly testing or sampling methods. Even the vertical method could be considered a sampling method. Step trench is a technique used in some contexts to negotiate the large archaeological mounds and prehistoric sites. The quadrant method was used by a few excavators, for the excavation of burials and stupas(Buddhist monuments), which are generally circular in shape. Should a burial have separate trench layout? The conventional approach has been site or antiquity or object oriented, and hence, importance was given to the quadrant method. However, normal grid method is enough to reveal the nature of burials from a landscape perspective. The open area excavation is done without leaving baulks or grids, which can fragment the archaeological sediments and the holistic nature of the contexts. However, leaving baulks is sometimes useful as they help understand the stratigraphy. The method mainly depends upon the nature of the excavation, and the focus is on how carefully an excavation is done, rather than the layout of the trench.

 

4.1 Augur or Coring Method

 

Augur or coring method is just a small sampling method and it can reveal about buried sites and it is used in underwater locations for knowing the potential of the sites that are covered with a lot of natural deposits. The augur and coring methods also can help in the case of prehistoric sites that are buried underneath the thick natural deposits. However, this method can destroy the archaeological remains, objects and architecture. It should be used judiciously and only when the conditions are inevitable. It is useful for retrieving samples from buried sites, and also from the lowermost part of the vertical trench where normal excavation would not be possible, because of lack of space. It is a sampling method used to understand stratigraphy. It is mainly used in geological and prehistoric contexts, underwater sites andburied sites. It is also useful sometimes in the lowermost levels of the trenches when the excavated area is limited, for understanding and prospecting the underlying natural sediments.

 

4.2 Trial Excavations

 

Trial excavation is a sample excavation method used to understand the nature of an archaeological site, its context and cultural materials, so that further action could be undertaken in future research and for formulating research problems and designing research. Trial excavation is often part of a regional research strategy, and this method can be used for several purposes.

 

Trial excavation is done before excavating a site on a large scale. As the name itself suggests the methodology here is to excavate only a small portion to understand the site.In order to test, if the food is cooked, one need not test each and every grain of cooked rice. Checking a few cooked grains would be sufficient. Similarly, the sampling technique is useful for understanding the broader picture at a particular site.

 

Trial excavation is only a trial and it may be taken to represent the nature of occupation at the entire site.Trial excavations done with utmost care at several sites can produce much different set of data than the horizontal or vertical excavations conducted at a particular site. Therefore, trial excavation should be seen as an important method for understanding the cultural sequences from a regional scale. In this method,normally digging is done manually, unless there is a thick natural deposit lying above the cultural deposit.In such context, machinery (earthmovers) could be used to clear non-cultural sediments on top of the site.

 

Selection of the Site

 

The site selection for trial excavation depends upon the objectives of the excavation. Normally, the trial trench is excavated in the top-most point of the site to understand the total cultural sequence of a site.These trenches can also be excavated in the boundary and in any area of the site or landscape that is suspected to have archaeological materials or other types of data.Sometimes, even after reaching the natural soil below the cultural layersat a site, the trial excavation is undertaken in order to understand the natural stratigraphy below the cultural layers.It can be used to trace the continuity of brick structures that are exposed in the trench, in other areas of the site. Similarly, the continuity of fortification and moats could also be tested using this method.

 

Area of the trench

 

Normally, the trial trenches may vary in size depending upon the size of the deposit. It can vary from one square meter to five by five square meter in area.Since trial excavation is done as a sampling, it can be undertaken in a short time with limited resources. A site always has buried materials and the surface features may not easily reveal what is actually buried. Therefore, excavation is inevitable in archaeological research. If a large scale excavation is planned and arrangements are made and if no potential is available, it could be a waste of time and resources. Therefore, trial excavation can tell whether a site would provide the necessary data expected to solve a research problem.It gives clues to the nature of the materials found and helps in the preparation for large scale excavations:

 

  • Requires limited resources: Time, Financial and Human Power

 

It can be limited in scope as the area of excavation may vary between oneand five square meter. Therefore, the resources required are limited.

 

  • Helps determine the boundary of the site

 

A series of trial trenches at a site could help determine the boundary of a site or settlement. Rather than surface indicators, trial trenches are best option to understand the limits of human occupation at a site.

 

  • Can be used to understand the stratigraphy at off-sites

 

Trial trenches in the off-site areas, away from core settlements, such as tanks, cultivable fields and other natural landscapescould help collect environmental data and ecofacts and to understand the landscape archaeological context of sites.

 

  • A valuable tool for regional survey and regional understanding of cultures

 

Trial trench method can be used across several sites in a region in combination with surface surveys to understand regional cultural sequences and cultural landscapes. Such a study would give a different, more valuable set of data than single site oriented excavations.

 

Limitations of trial excavations

 

The trial trenching approach has its own limitation and it cannot be a substitute for verticalor horizontal excavation. Therefore, the interpretations of data from the trial trenches should be used cautiously.

 

  • Only gives very fragmentary data about the site

 

The data from the trial trench cannot be extended to the entire site, since the trial trench represents only the sedimentary layers found in a particular, i.e. excavated, area.

  • Disturbed Area

 

If a trial trench is located by chance in a large disturbed area (with refill) such as a well, it might not give an accurate picture of the site.As mentioned above the complete picture and activities at a site cannot be understood just by trial excavations and the area selected for the trial excavation may not produce representative data.

 

Possible Solutions

 

One possible solution to overcome the limitation of the trial trenches is multiple trial trenching. Multiple trial trenches can be useful in the understanding of a site. However,this method cannot be treated as a substitute for vertical and horizontal excavations.

 

4.3 Vertical Excavations

 

Vertical excavation, as the name suggests is intended to understand the vertical cultural sequence of a site. In the conventional method, the vertical excavation of the trenchesare laid in a pattern of lay out that cannot be extended laterally. However, a site, after gridding the area, a series of grids may be selected for vertical excavation. The vertical excavation is intended for understanding cultural sequence and chronology of the site. It is generally limited to a few trenches. It should not be seen as an entirely distinct method from the horizontal excavation and the documentation and recovery of the material remains should be done with great care in both the excavation methods.

Advantages

 

Vertical excavationfocuses on the cultural sequence of a site and hence, it aims to understand all the cultures present in a site. It requires limited time and resources when compared to the horizontal excavations. It can help to understand the cultural history and long term variations in cultural life patterns of adaptations. It is ideal for understanding long-term cultural developments of a region.

 

Limitations

 

Vertical excavation is useful for diachronic perspectives, it may not be very helpful to develop a holistic understanding of a particular culture and its contexts. Because, the focus in this methodis on long term cultural developments. Spatial organization within a specific cultural context cannot be understood using this method. Therefore its limitation lies in its fragmentary approach, but it can help in reconstructing the long-term chronological sequence in ceramics and tool typology and technology.

 

Another problem with the vertical method is there is nocertainty that all the cultural periods are represented in a particular locality of a site that was chosen for excavation. For instance, in one specific time period people might have shifted their activities to another locality and the activities of this cultural period may not be found in all areas of the site.Therefore, vertical excavation cannot be a substitute for the horizontal excavation method.

 

Another limitation is the fragmentationof evidence; since vertical excavation concentration of the long term perspective, certain activity areas in a context may be partially recorded and/or destroyed in the intention to go deeper, and to find the earlier evidences. However, the horizontal method would focus on the documentation of the evidences from a holistic context and then it would proceed deeper.

 

In the case of very important architectural remains or cultural features found in a context, the evidence has to be documented properly, and then lifted (salvaged) to a locality before proceeding for further excavation. Nowadays in the excavation methods heritage component is also taken into consideration, since the idea of site museum and local development are stressed in many contemporary social contexts.

 

Solutions

 

Vertical and horizontal excavations cannot be seen as entirely distinct methods. Ideally, the vertical and horizontal excavations have to be combined for a better understanding of an archaeological site.

 

 

 

4.4 Horizontal Method

 

The horizontal Method is used for understanding the complexity of spatial organization at a site.The horizontal Method of excavation is discussed in detail in a separate module. Hence, a brief outline is presented here. Horizontal method is used for the excavation of a large area. In this method the trenches are laid in the form of grid or boxes as laid at Arikamedu by Mortimer Wheeler. It is used in the excavation of fortification and towns covering a vast area. The grid method is also known as Wheeler-Kenyon method.

 

Open area method is also a horizontal method. In this method, baulks are not left between the small trenches. The entire area is excavated as one trench

 

Step Trenches

 

What is a step trench? Step trenches are useful in the case of large mounds. Step trenches are laid out in an area to understand the large mounds and in prehistoric contexts. The trenches are excavated in steps so that the total stratigraphy of the mound can be sampled at select locations.Here the whole mound is not excavated. If deep trenches are excavated, the sections may collapse and hence, step excavation method is adopted.

 

 

Advantages

 

Step trenches can help reduce the cost of excavation in certain areas, while they give the overall perspectives of the mound.It can be used in large mounds with prehistoric remains.It can help at sites where the sections might fall because of the loose nature of the cultural deposits

 

Limitations

 

Step trench can only reveal certain aspects of an archaeological mound. This method is not suitable for understanding the sites with a lot of cultural materials. This method cannot be substitute for the complete excavation of a mound. It can be mostly applied to the prehistoric site and where there is no other option to excavate the mound completely

 

4.6 Quadrant Method

 

Quadrant method is used for the excavation of burials and stupas which are circular in shape. The circular area is divided into four quarters/quadrants. The quadrants are fixed in with baulks towards the cardinal directions. Excavation is first taken up in diagonally opposite quadrants first, and then excavation is taken up in the rest of the two quadrants. In the excavation of the burial sites, the area in between the burials should also be excavated so that the complete land use could be understood. For example, themegalithic site of Anakkara in Kerala produced evidence of habitation in between the burial area.

 

5. Discussion and Summary

 

The vertical and horizontal methods actually refer to the layout of trenches, and the area of excavations and the broader focus. The method of excavation involve apart from the layout of trenches, the techniques of removing and recording the soil layers, architectures, features and artifacts and their context.The choice of the excavation method depends upon the nature of the research problem and the resources and time available.

 

Trial excavation is preliminary in nature and may be conducted as part of regional survey before planning for large scale excavation. Trial excavation would also be useful in combination with the regional survey, if trial trenches are excavated across several sites in a particular region.

 

Vertical excavation is a more detailed exercise than the trial excavation. It is preliminary and is also a sampling method for a large site, and it is suitable for the reconstruction of regional cultural sequences. Vertical and horizontal methods should not be seen as distinct and they are complementary to each other. The documentation and recovery of the materials remains should be done with great care in both the vertical and horizontal excavation methods.

 

Step cutting is a method of trenching, chosen depending upon the context and the objectives. It can be used in the context of prehistoric sites and in the contexts of large mounds where the trench section could collapse due to loose nature of the sediments and larger size of the mounds.

 

The excavation method is related to the research objectives and the other components of the research project and different methods need to be adopted to suite the research problem. No single method can give a complete understanding of an archaeological site.A combination of vertical and horizontal methods is necessary for a better understanding of sites. The choice of the excavation method depends upon the nature of the research problem and the resources and time available with the excavators.

 

Appendix 1 Tools and Implements for Archaeological Excavation

 

A few of the important tools widely used for excavation are given below. They vary from region to region and the regional conventions and the approaches of the excavators.

 

  • GPS – Global Positioning System for geocoordinates, orientation and mapping

 

Fig. 8 A GPS Device

 

  • Hard, durable paper labels for bagging the artifacts and writing contexts
  • Cloth/plasticbags for collecting pottery
  • Plastic or clothmounted paper covers for antiquities
  • Cotton – for packing delicate objects
  • Stationery:Paper, pencil note books, scales, scissors, papers for mapping, staplers, pinsand other objects
  • Pencil, markers, pen, permanent marker, and paper – great for notes, documentation, labelling.
  • Tape measures : 2m, 5 m, 20 m, 50, 100 m for measurement
  • Boxes for antiquity storage
  • Trowelof various sizs for excavation
  • Knives ofvarious size for excavation
  • Pick axe of various size for digging
  • Brushes of various size and hardness for cleaning
  • Wheelbarrowfor transporting soil

 

  • Sieve (screens and sifters) for sieving the soil
  • Shovels for clearing the soil
  • Buckets, dustpans, baskets for transporting the excavated soil.
  • Wood for frames for sieves and screens
  • Meter scale for photography
  • Compass for orientation and survey
  • Line level for finding the level
  • Dentist tools/Dissection tools for excavation of delicate features
  • Wooden or Iron Pegs for trench marking
  • Ladders for movement in the excavated area
  • Camera and Video
  • Arrow scale with North for documentation
  • Stand for Photography
  • Large tarpaulinsfor covering the trench in case rain
  • Camp Equipments, medical and other materials for camping