Exploration is  the method by which archaeologists try to detect unknown sites,  and incase of known sites try to know the potentiality of the site by applying various techniques.  In pursuit of such investigations we have to depend on various means and methods.


            Partially accidental and involuntary discoveries are known as chance finds, many times lead to the discovery of ancient sites.   Chance finds occur as a result of work undertaken by human agency or by natural forces.  Natural erosion has several times exposed the first traces of lost sites.  Wind and water are the chief elements which contribute to natural erosion, leading to exposure of a site.  Rain, in the form of streams, cut through the ancient sites and thus expose different strata and the structures and the material im\bedded in them.  The rivers changing their course and the seas cutting the shores also many times reveal hidden sites.  Similarly, a fall in the level of a lake can expose previously submerged sites. It was in this way that the lake village of Zurich (Switzerland) was discovered.

            Human  activity  is more varied  than that of the nature.  The diggings for foundation and road laying have brought to light  numerous archaeologioal sites. The great  Indus valley site Mohonjodaro was discovered while laying railway track.   The accidental discovery of numerous coins  and  sculptures is  well known.


            All the methods of prospecting are base on one  principle – all remains which cannot actually be seen leave some kind of trace of their presence by virtue of  the fact that they existed at a a given moment.  The methods of surveying can be studies under the following heads.


Ancient literary works contain lot of information regarding ancient townships, pilgrim places, important routes etc.  All kinds of literary works can contribute to the search for sites,  but more important are the topographical and geographical works.  The great Indian epics  Ramayana and Mahabharata and the works Kalidas ,  Kalhana, Herodotus, Megasthenese,  Fahien, Itsing etc,  have contributed greatly not only in identifying the ancient cities and religious centres but also their extent and condition.  (eg. Pataliputra, Hastinapura,  Kaundinyapura,  Sanchi, Ujjain, Vijayanagara,  Tamralipti,  Barukacha).


     Both ancient and modern maps helps us in locating vanished sites and monuments.  Ruins marked on ordinance survey maps are very useful in locating ancient monuments.  Features like temples,  dolmens,  caves,  etc.  marked on the maps are very useful in the search for ancient sites.  It is also important to study geological and geographical features like mountain, 

soil formation  and water sources for proper exploration of an area,  as these features greatly influenced the settlement pattern of the ancient cultures.  Rich  natural resources,  especially water and fertile soil were the chief deciding factors that influenced the location of ancient habitations.  So an understanding of such places with the help of  maps is important before undertaking any exploration for ancient sites


     Place names have great significance in the archaeological exploration as they often help in locating ancient sites.  For example in  Andhra  Pradesh and Karnataka places having names relating to ash such as Veebhuti  Halli,  Veebhuti padu,  Budidapadu,  Budidapallik,  etc.  Have yielded ashmounds of  Neolithic period.  It was also observed that place names ending with padu,  Penta and Dibba often indicate presence of some ancient site in the vicinity.  Similarly places with   Buddha,  Muni Rish,   Devuni etc,  are know to contain some Buddhist or Brahmanioal monuments.  Therefore,  a careful study of the place names is very  important in the explorations for ancient sites


     Surveying at ground level is the most traditional and the most direct form of prospecting  as it presents real picture and potentiality of the site under investigation.  In its most basic form , surveying at ground level is carried out on foot. The advantage of survey on foot is that a person can  pick up potsherds,metal artifacts, coins, stone tools, etc. Which are indicators to the presence of a site. Survey of a  region can be taken different objectives.  Depending  on the problem selected,  the nature of  survey also changes  as  described below.     


For locating prehistoric sites like palaeolithic  and Mesolithic sites like palaeothic and in abundance are the most potential areas.    We have also to concentrate on water sources and natural rock shelters and caves as these must have served as resting places for prehistoric man.  For locating   Neolithic sites,  it has been observed that ,  Neolithic people were good agriculturists. 


     When on the look-out for protohistoric sites,  we have to again  concentrate on fertile lands of river deposits and valley.  But ,  it does not mean that these sites could be found only in such localities.  For example Kalibangan,  and   Indus culture site is in the desert  of Rajasthan.  For exploration of early historic and historic sites we can rely more on ancient literary works like Ramayana,  Mahabharata  and the Buddhist and   Jaina literature.

     But,  more important aspect awhile  taking up explorations for any kind of sites is to   acquire information regarding the already know  type sites of the region selected .  An archaeologist should know what kind of antiquities and pottery are expected from which type of sites.


     This method was first applied to detect archaeological structures by Prof  R.J.C.  Atkinson in 1946.  Electrical surveying uses the same variations in humidity which are also applied to the damp-marks detected by aerial photography.  Moisture has the property of conducting  electricity,  which passes through the mineral salts dissolved  in the water.  So the wetter the soil, the more readily the current will pass through it,  and the dryer the region,  the poorer the conductivity of the soil.  In pits of ancient ditches, which collect moisture in the earth, resistance to the electrical current will be weak.  Conversely, a quickly drying stone wall or a footpath will be stronger.  For resistance surveying four electrodes are fixed in equal distance in  a line.  The two outer electrodes measure the voltage being applied and the two inner electrodes are used to measure the resistance.   Alternate current is used to eliminate the electrical charges being formed in the soil strata.   If the eath between these two electrodes is abnormally resistant or abnormally conductive (unresistant),  the measurements will show irregularities on the resistance graphs drawn to record them.   When the selected line is completed the resistance along a parallel line is measured and so on.  A comparison of the successive graphs obtained in this way may reveal a construction fairly accurately. This method was successfully used at Naikund in Maharashtra which resulted in the discovery of an iron smelting furnace.


            This process urns into difficulties, when it encounters natural pockets of clay or earth in the rock. Stoney soil conceals remains and makes the placing of the electrodes difficult, and rain and pits of organic matter can falsify the results.


            Magnetic surveying is based on the modification of the earth’s magnetic field by the magnetism of various sources and other buried remains. It is known that if clay is heated  in an oven or intense fire, it acquires a magnetic force of its own, and retains it after it cools down. In practice the caly contains varying quantities of ron oxides such as magnetite or hematite, which cause its red colour and their magnetic field align itself with that of the earth as the temperature rises, and remains aligned when the clay cools off again. The result is a localised magnetic disturbance in a given area, the intensity of which can be measured with a magnetometer. This technique is known as thermo -residual  technique. A systematic series of measurements taken on a regular grid covering an area will show irregularities due to the presence of a furnace, a patch of burnt earth or a potters kiln. The irregularities in the curves can indicate the size and depth of the buried structure.


            Acoustic surveys are traditionally carried out by banging the ground with an iron bar, which gives off a hollow or solid sound when it hits the ground and can indicate presence or absence of structures below. Likewise seismic surveying which consists of recording on a seismograph shock waves set up in the earth, can also indicate buried structures. These methods are mainly used after detecting a site to know the nature of the mound and to estimate the extension of the walls and structures before undertaking excavations. This technique is useful in selecting suitable area for excavation.


.           Probe checking is done by T-shaped rods driven in or screwed down by hand to the desired depth and then drawn up again. The presence of soil changes can point out to a grave or habitation site. But most of the archaeologists are against this method as although this process is harmless enough above a house floor it can be imagined how destructive it could be in the case of a tomb, where such blind gropings could cause irreversible damage to the skeleton or the grave goods.


            This is similar to probe checking, but here instead of probes a hole is drilled in the suspected area of hollow structures and tombs and a miniature camera and flash gun housed in steel tube is introduced into the drill holes to take photographs of the interiors. Alternatively,  a  periscope also can be used to inspect the contents. In this way a quick estimation could be made as to the contents of the grave. This helps in working  out an indestructive approach to the structure or tomb in case of its excavation.


            Chemical surveying is chiefly founded on the analysis of phospates. It is observed that the percentage of potassium nitrates and phosphoric acid increases at the places of human settlement. Chemical analysis of the soil can reveal the presence of prehistoric habitation sites. More potential areas for this analysis are the caves and the rock-shelters where prehistoric man might  have dwelt for considerable time.


            Aerial photography or aerial surveying is a very useful method in locating ancient sites and monuments. By this method a large area can be surveyed quickly. By this method closely overlapping photographs are taken by special camera, so that nothing is missed and also for subsequent stereoscopic examination. To take aerial photographs an airplane is flown over a selected area covering parallel strips of land till the whole area is covered. From the photographs  taken in this manner we can easily identify features looking round, square or rectangular, which probably represent some ancient structure. Ancient habitations could be easily identified due to the discolouration of the mound in comparison to the surrounding area. Completely buried structures also can be identified by observing the differences in relief, though very slight, caused by these buried structures, which throw shadow in oblique lighting conditions (morning and evening).

Crop-Marks:  Crop-marks or variation in plant growth can occur in different ways depending on the nature of the remains beneath. Above a wall, for instance, where water cannot readily penetrate, the growth of vegetation is thinner than over a ditch which has good drainage. Consequently vegetation gives the reverse picture of the things buried underground. Similarly plants above a wall tend to look pale as they do not get enough nourishment due to the inability of the roots to penetrate deep into the soil. An aerial photograph clearly reveals the variations in plant growth and the discolouration. Thus aerial photographs can supply a varitable X-ray pictures of the ground.

            For aerial photography, great care is necessary in choosing the time of the year, the weather, and the time of the day. The shadows thrown by minor variations in contour are much prominent when the light is lower and more oblique. The source of light for aerial photography being the sun, the photographs must be taken early in the morning or late in the evening. Aerial photographs are particularly more revealing, few days after rain.

            Though aerial surveying is not very common in India it has been successfully used in studying the town planning of the Indus cities. Similarly the fortifications of the ancient city Sisupalgarh was studied using the aerial photographs. In Andhra Pradesh an accidental discovery of a Buddhist site at Bavikonda occurred while aerial surveying was being conducted by the Indian Navy for security purpose.


            The limitations of the aerial  survey are that, some times even modern sturctures also may be identified as ancient ones. Similarly, shades cast by clouds may conceal features and may even show false discolourations. Some features may not be so prominent as to be detected in aerial photographs. Hence caution should be exercised and cross checks necessary before arriving at a conclusion.