been applied in and around two small sized pyramids of Hellenikon and ... The present results question earlier attempts classifying these pyramids at the.
G E O P H Y S I C A L P R O S P E C T I O N , A R C H A E O L O G I C A L EXCAVATION, AND DATING IN TWO HELLENIC PYRAMIDS E S. THEOCARIS 1, I. LIRITZIS2, E. LAGIOS3 and A. SAMPSON4 IAcademy of Athens, P.O Box 77230, Athens 175 10, Greece; 2Research Centrefor Astronomy and Applied Mathematics, Academy of Athens, Athens, Greece; 3Department of Geophysics-Geothermy, University of Athens, Athens, Greece; 4Ministry of Culture, Department of Antiquitiesfor Cyclades, Athens, Greece
Abstract. Geophysicalprospectionemployingmagnetometryand electromagneticmeasurements has been applied in and around two small sized pyramids of Hellenikon and Ligourio in Argolid, Greece. The magnetic anomalies appropriately assessed were interpreted as possible archaeological targets. Subsequent test excavations revealed the presence of room foundations and parts of walls, as well as a plethora of ceramic ware. Typological study of the ceramics classified them to as early as the proto-Helladic period and to as late as the first centuries A.D. The earlier periods have been also confirmed by a novel application of thermoluminescence (TL) dating of ceramics and the megalithic stones themselves. The present results question earlier attempts classifying these pyramids at the Classical period and favourmuch earlier periods. Key words: Pyramid,magnetics, electromagnetics, archaeology, pottery, Helladic, Hellenistic, Classical period, excavation, thermoluminescence (TL) dating.
1. Introduction The pyramid is an architectural structure with a long time history. Its typical form is known mostly from Egypt, while in Mesopotamia similar structures are the ziggurats, which are in fact a variant of the truncated pyramid (Petrie, 1938; Edward, 1961; Fakhry, 1969; James, 1972; Michalowski, 1972). Pyramidal elements are also found in the chalkolithic structures of Minorca in the Balears (end of the 2nd to beginning of the 1st millennium B.C.), while the general pyramidal form continues to appear much later in time with the step pyramids of central and south America. It is worth noting that the pyramidal form is normally not related to common everyday uses, but to sacred rites concerning heaven and celestial bodies, as well as, to the definition of time. The construction and use of special buildings for watching celestial bodies as early as the 4th and 3rd millennium B.C. is also suggested for the temples of Malta, one of the best-kept secret in Mediterranean archaeology, presumably built according to astronomical orientations (Serio et al., 1992). The oldest known up-to-now pyramidal structures in Mesopotamia and Egypt are dated to the 3rd millennium B.C., while those of America appear at about 300 B.C. and continue up till the 2nd millennium A.D. On the other hand, construction of special megalithic structures, such as those in Stonhedge, Britain, and in Camac, Surveys in Geophysics 17: 593~18, 1996. 9 1996Kluwer Academic Publishers. Printed in the Netherlands.
594
1,. S. THEOCARIS ET AL,
Plate 1. View of Hellenikon pyramid.
northern France, and the abovementioned temples of Malta, presumably are related to astronomical or religious purposes (Roche, 1985). Pyramidal structures in Greece are very poorly attested. Two at least examples are known from Argolid in Peloponnese (Plates 1 and 2). This type of structure is reported by ancient Greek traveller Pausanias (Papahatzis, 1976), a fact which had stimulated a first archaeological survey in the Argolid by Wiegand in 1901 and later by Lord and Scranton (in Lord, 1938). According to Pausanias,the Hellenikon pyramid was erected as a memorial after the battle, which had taken place at that very same area between Proetos, King of Tiryns, and his twin brother Akrissios, King of Mycenae, and where shields were used as defending weaponsfor thefirst time, not only for these kings, but for all the soldiers participating in this fratricide battle. In commemoration of this event rows of shields have been hewed onto the limestone walls of the one pyramid, as a memorial of this innovation. Here took place a fight for the throne between Proetos and Akrissios, the battle they say ended in a draw, and a reconciliation resulted afterwards as neither could gain a decisive victory. The story is that they and their hosts were armed with shields, which were first used in this battle. For those that fell on either side was built here a common tomb, as they were fellow citizens and kinsmen (Pausanias, Korinthiaka in Papahatzis, 1976).
GEOPHYSICALPROSPECTION,ARCHAEOLOGICALEXCAVATION,AND DATING
595
Plate 2. View of the partly demolished Ligourio pyramid.
Both, the legentary nomenclature by Pausanias, as well as the reference to the first use of shields, transmits chronologically the incident to the pre-homeric times, presumably throughout the Early Bronze age (3000 to 2000 B.C.) However, these pyramids have been dated to the 4th century B.C., based exclusively on a small number of ceramic sherds found inside the one pyramid, and they were thought to have been used up to the first centuries of Christianity. Since there was no satisfactory proof of the dating a building from dating a small amount of ceramic sherds found inside it, it was judged necessary to reassess more thoroughly the dating of these buildings. Indeed, the complete lack of systematic excavation and any other detailed study cast considerable doubts concerning their exact date and their use. The subject is of considerable interest by itself, and of great importance to reappraise it on the basis of a corroboration between archaeometry and archaeology and the new achievements in these cognitive fields. The application of geophysical methods ofprospection was first applied in and around the two pyramids, followed by archaeological trial excavations. Subsequently, the unearthed finds were typologically classified and dated by thermoluminescence (TL). At the same time the dating of construction was made employing the novel application of TL (Liritzis, 1994). The use of various geophysical methods in support of archaeological field investigations often most contributes to the detection of burried targets of interest (e.g., relevant papers in the journal ProspezioniArcheologiche, vols. 7-8, Linington, R. E. (ed.), Lerici Foundation, Rome, 1972-1973; Tsokas et al., 1994; Aitken, 1974;
596
E S. THEOCARIS ET AL.
Tite, 1972; Clark, 1990). The successful application of geophysical prospection is due to the recent advancement in the development of geophysical instrumentation, as well as that of computer software and hardware. This paper demonstrates the results of both combined geophysical surveys, including total-field magnetic and Electromagnetic (EM) measurements, and archaeological excavations, whose locations were suggested by the geophysical results. The work was conducted at two archaeological sites in Argolis (Peloponnese). These two sites are the Hellenikon pyramid (Plate 1) and the Lygourion demolished pyramid (Plate 2). The geophysical measurements were collected over relatively small grids around these ancient buildings with the objective of locating geophysical anomalies possibly associated with buried archaeological remains. Selected anomalies were further investigated by limited-scale excavations. As the ultimate objective was to establish the age of construction of the pyramids, pottery and architectural remains have been analysed and dated using recently developed techniques.
2. The Geophysical Measurements Two geophysical methods were applied. The magnetic surveying method was the one, which was applied to a larger extent, compared to the electromagnetic (EM) one, which was employed only selectively at a few only occasions and along profiles to facilitate the interpretation of the magnetic observations (Nettleton, 1976; Telford et al., 1976; Tsokas et al., 1994)). The proton magnetometer was initially preferred, for the present investigation, as an efficient, accurate and quick prospection method. It has a great sensitivity (1 gamma or better), absolute accuracy, no moving parts, and measures total field intensity with freedom from orientation errors. In a later stage we intent to apply electrical resistivity, as well, for comparison. The principle of the magnetic method is based upon the magnetic inhomogeneity of the upper crustal layers of the Earth. This inhomogeneity is caused, in the presence of relevant iron minerals, by the uneven distribution of the ferrimagnetic minerals (maghemite, haematite, magnetite) or related minerals (ulvospinel, titanomagnetite, itmenite, pyrrhotite), within the various geological or archaeological formations (Ferrimagnetism being related to the ferromagnetism which produces the permanent magnetism associated with metallic iron). This uneven distribution assigns different susceptibility values, causing local magnetic anomalies in the total magnetic field (magnetic contrast of soil, ruins, kilns, stones etc,). These small local disturbances (expressed in the magnetic units of nanotesla, nT) can be measured accurately (better than 9 1.0 nT) by the use of the proton precession magnetometers. Total field proton magnetometers, type G-856 by GEOMETRICS, with a digital memory storage capacity, were used for the magnetic surveys. The APEX instrument was used for the EM measurements along profiles, which were selected to assist the interpretation of the magnetics. This instrument basically
GEOPHYSICALPROSPECTION,ARCHAEOLOGICALEXCAVATION,AND DATING
597
measures the electrical resistivity variations to a depth of about 3 m, depending on the conductivity of the superficial layers. Both, a transmitter (5 KHz) and a receiver are mounted on the ends of the instrument having a length of about 1.6 m in a position of horizontal dipole. The transmitted signal within the ground, depending on the electrical properties of the superficial layers (e.g., electrical contrast of soil, ruins, stones), induces secondary EM fields, which are registered by the receiver as 'in-phase' (real component with a direction parallel to the direction of the initial EM field) and 'out-of-phase' (imaginary component with a direction 90 ~ with respect to the initial EM field). Therefore, the various superficial geological and archaeological formations, having different resistivity values, finally induce analogous EM fields. A high quality resistor creates an out-of-phase secondary field, comparable to the initial EM field, while a sensitive conductor forms a secondary field almost in-phase with the initial field. Formations of intermediate conductivity values will show up parts of both components. The greater the ratio (in-phase/out-of-phase) the larger the conductivity of the formation (target). The EM was used as a corroborative instrument along with the proton magnetometer, and as a means of testing its efficiency, in such archaeological sites. 2.1. THE HELLENIKON PYRAMID
Near the Hellenikon village in Argolis (Peloponnese) and on a small hillock, there is a construction of pyramidal shape (Plate 1)) of orthogonal dimensions (about 15.0 m x 13.0 m) It is in a well preserved state except that its upper part is rather destroyed. The geophysical surveys took place around the building, as it is shown in Figure 1. The area on all sides of the pyramid were covered (Figure 1). Magnetic measurements were collected at a 1-m grid spacing, bearing in mind the expected burial depth of possible archaeological targets of less than about 1 m. Beneath this depth lies the limestone bedrock of the hill. The largest grid was the one located to the east to the pyramid, with dimensions of about 60 m x 40 m. The magnetic measurements, which were taken with the sensor at the elevation of 1.0 m from the ground surface, are referenced to four different base stations and the data were drift (diurnal magnetic drift) corrected. Thus, the magnetic values of the four grids (Figure 1) have independent frames of reference, and the amplitudes of the magnetic anomalies cannot be compared. The same is also true of a (7.0 m x 7.0 m) area inside the pyramid, which was covered by magnetic measurements at 1.0 m grid spacing. The total-field magnetic anomalies of the sites covered magnetically are presented in Figures 2 and 3. The area west of the pyramid does not show any significant anomalies of interest (Figure 2). There are, of course, a few isolated anomalies at the southwestem, northwestern and northeastem parts of the grid [with coordinates: (2 m, 1 m), (10 m, 7 m) and (1 m, 5 m--6 m-7 m)] but these are of very small wavelength and amplitude. Their source has rather very limited dimensions,
598
E S. THEOCARIS ET AL.
3Bin
F
oT IN 20m
Pyramid Base
l=
l= oo
---20m
3Bin
Figure 1. Diagramatic representation of the area of Heltenikon pyramid, around which magnetic prospection was performed. Squares indicate excavation trenches A, B, C, D, E, F.
and represent rather scattered metal objects (e.g., horseshoe, tin cans), found in all grids. In general, there were no indications of important subsurface formations. The area south of the pyramid exhibits more interest than the previous ones. It can be seen that there are distinct isolated anomalies at its southern and central parts (Figure 3a), with coordinates (8 m, 14 m), (12 m, 2 m-4 m), and (9 m, 16 m); these are, however, of small amplitude and are associated with the existence of a pile of rocks at the ground surface, and an outcropping of a large limestone building block, respectively. At the northeastern part of the area there is an elongated magnetic anomaly of a small amplitude, with a north-south direction. It is truncated by another small amplitude anomaly in the E-W direction, which seems to continue
599
GEOPHYSICALPROSPECTION,ARCHAEOLOGICALEXCAVATION,AND DATING
AREA '""-"" vv-_.~l OF PYRAMID I
I J
'/
t
""i'i, . . . . . . 7 - " -
1 !
,
I I ! I
1
!
! !
,
A
!
Z
~I
!
T !
!
I
I
i:
/:
! I '
t ~ . . . . . . .
!
! T
1
7
|
"|
I/
" / / /
I
f
!
s
I
o
i
,v
~
E-W
l
9
I
~
9
&
!
L2
DISTANCE
Figure 2. Total-field magnetic anomalies west of the Hellenikon pyramid, indicating trenches A, B. Contour lines are isoanomalic curves of equal magnetic field, corresponding to levels of 4 nT.
600
R S. THEOCARISET AL.
AR~'~ SOUTH
i,i z Go t'm
I z
'o
4
B
12
~
~o
E-W DISTANCE Figure 3a. As for Figure 2 but for the southern area of the Hellenikon pyramid. (isoanomalies of 4 nY).
to the east. The last positive anomaly of interest has an amplitude of 8 nT and might be associated with the existence of an elongated burried feature, with coordinates (16 m-20 m, 8 m). The area north of the pyramid has a very irregular topography, and some of the magnetic measurements (Figure 3b) were made at a few points, where the ground surface had a large slope. The most interesting magnetic anomaly is the closed anomaly of 10 nT, which is located at the most northern part of the grid. This positive anomaly is probably associated with a subsurface existence of a limestone rock formation, or other feature. The latter suggested an investigation by a small
GEOPHYSICALPROSPECTION,ARCHAEOLOGICALEXCAVATION,ANDDATING
601
AREA NORTH OF PYRAMID 0
2
6
4
8
10
12
22
22.
20
20
18
18
!6
16
14
~D
ID -.--,- 12
12
LIJ 0 Z . < 10 p... (/3
lO
8
. . . . . .!. . . I
I
4-
0
2 W-E
I
......
;--: 4-/-,4
J
I
I I
I
I I
1"-%'~''7 . . . .
I
3 .....
!
I
4
8
10
DISTANCE
6
12
(Meters)
Figure 3b. As for Figure 2 but for the northern area of the Hellenikon pyramid. (isoanomalies of 3
nT).
scale excavation (trench E, see 3.1 below), which indeed revealed a plethora of prehistoric ceramic sherds. The area east of the pyramid (Figure 1), comprising the largest part of the surveyed area exhibits special interest. The scattered magnetic anomalies (Figure 3c) have distinctive shapes and amplitudes, which may be associated with burried
602
P.S. THEOCARISET AL.
AR-SA EAST OF PYRAMID
" ~ 32
32
30 28
30 28
26
26
24 22
24
O0 20 I 18
ZO 18
216
16 14.
L~ r Z
