Seeing Beneath the Surface at Giza
by Glen Dash
Archaeological excavation is slow, painstaking work. Remote sensing
can be a helpful adjunct with its indirect look below the surface based on
geophysics. In the fall of 2003 we put some remote sensing techniques
to the test in a pilot season of the Giza geophysical survey, sponsored by
the National Geographic Society with AERA (Ancient Egypt Research Associates),
the University of Birmingham’s Institute of Archaeology, and the California
firm of Tremaine and Associates. Here, Glen Dash, an AERA board member
and Research Fellow at Boston University’s Center for Remote Sensing, describes
the work carried out by Tremaine and Associates. – Mark Lehner
The basic technology needed to see beneath the soil has been around for
decades. “Remote sensing” tools such as magnetometers, surface penetrating
radars and electromagnetic induction machines are routinely used in geological,
environmental, and criminal investigations. But their use in archaeology
has been relatively limited. Part of the reason is their complexity.
In order to do remote sensing well, the operator needs to know something
about electromagnetism, geology, and archaeology all at the same time.
One goal of our 2003 geophysical pilot season was to bring together people
from all these disciplines to explore unexcavated areas of the Giza Plateau
with remote sensing tools. With National Geographic sponsorship and
in collaboration with Dr. Zahi Hawass and the Supreme Council of Antiquities,
AERA assembled a multi-disciplinary team that included AERA crew members
and staff from Tremaine and the University of Birmingham. The Birmingham group
carried out radar and magnetometry surveys of part of the areas covered by
Tremaine plus a survey of the area north of the Khafre Causeway. Glynn
Barrett did a survey of the Menkaure Pyramid and Queen’s Pyramid GI-C using
LiDar, a laser scanning technique. In this installment we report only
on the Tremaine survey using electromagnetic conductivity.
Tremaine uses equipment that “sees” beneath the surface with “electromagnetic
induction” (EM). In the simplest terms it works as follows. A
transmitting device is suspended over the ground, which generates an electrical
current that flows into the soil. A receiving device, located nearby,
“reads” the current flowing in the ground. The ground current varies
depending on the materials in the soil. Some materials conduct electrical
currents readily, such as clay; others impede it. An abrupt change
in the current, called an “anomaly,” may signal the presence of a structure
or a wall.
We selected a number of areas across the Giza Plateau for remote sensing
(Figure 2). Some of these were of special interest
to our project, or of interest for understanding cultural features on the
plateau. The team chose some locations as test sites. Only a
portion of the surveyed area is discussed here since the data are still being
The Khentkawes and Menkaure Pyramid Valley Temple Towns
In 1932 and 1933, Selim Hassan found an orderly collection of houses that
lined the causeway running east from the tomb of Khentkawes, a queen who
lived at the end of the 4th Dynasty. (See AERAGRAM 5/2, Spring 2002.)
When Hassan uncovered the walls, they stood chest high and still bore traces
of red, white, and black paint. These features were not backfilled and
over the intervening 70 years they deflated, leaving little remaining today
except for dark patches on the ground.
Nearby is the Menkaure Pyramid Valley Temple. George Reisner began
excavations here in the summer of 1908 and found a temple that had been in
service from the 4th to 6th Dynasty. During that time it had been destroyed
by flooding, was rebuilt, and then invaded from the east by small irregular
houses and granaries. Sand layers intervene between the 4th and 6th
Dynasty levels testifying to a period of neglect or abandonment. Because
these two sites had been previously excavated, they served as ready test
beds for the Tremaine technology.
In Figure 3 Tremaine’s data are superimposed over
Hassan’s 1932-’33 map. The features found by remote sensing correspond well
to the structures Hassan mapped in the Khentkawes town. The northern
and eastern walls of the Menkaure Pyramid Valley Temple also show clearly.
Within the rectangle lie possible Valley Temple structures or perhaps artifacts
resulting from Reisner’s backfilling. He did not excavate the whole
temple at one time but rather, excavated the western part first, then the
southern, backfilling the western area as he worked. He cleared the
court in the east and the northeast sections last, perhaps accounting for
the smoothness of the data in that area.
The Soccer Field
It is certain that the large Royal Administrative Building found in 2002
extends under the Abu Hol sports club (Area B in Figure
2). Excavations to date have mapped the northern end of this building,
exposing an area 25 meters in length and close to 50 meters wide. The structure
could be a royal palace dating to the reigns of Khafre and Menkaure.
Tremaine’s remote sensing results are shown in Figure
4. One obvious feature is the L-shaped anomaly, which seems to
align with the Royal Administrative Building. If the L is the juncture
of the building's south and west walls, then the structure would extend almost
100 meters from north to south. The feature is approximately one meter
below the surface, about the same height as the remaining exterior
walls of the building.
The Workers’ Cemetery
The “Workers’ Cemetery” (Areas C-1 and C-2 in Figure
2) sits on the eastern slope of the Maadi formation. Currently being
excavated by Dr. Zahi Hawass, the cemetery is thought to be the final resting
place for some of the workers who built or serviced the Giza necropolis in
the 4th and 5th Dynasties.
The remote sensing results are shown in the maps of C-1 (Figure 5) and C-2 (Figure 6).
Rectilinear anomalies dot the areas surveyed. The darkened anomaly
to the northeast in Figure 5 could be an outcrop of bedrock or a spoils pile.
As one moves to the south and west, the conductivity rises from a lower (yellow)
to a higher level (red). This could be a result of bedrock (higher conductivity)
dipping under a layer of sand (lower conductivity). The several rectilinear
features in the diagram may reflect tomb shafts or voids. In addition,
there is an abrupt transition from yellow to red forming a distinctive 90°
angle, possible evidence of quarrying.
At the southern end of the Workers’ Cemetery (Area C-2 in Figure 2) Tremaine’s surveys detected a number of features
along with one truly huge anomaly, approximately 50 x 15 meters, oriented
to the northeast-southwest. Areas of high conductivity probably reflect bedrock
close to the surface. Lower conductivity rectilinear anomalies may
indicate air or sand filled voids in the bedrock.
The Wadi, the Sphinx, and the Harbor
The Central Wadi (D in Figure 2), lying between
the Mokattam and Maadi formations, probably served as the principle conduit
for non-local materials used in pyramid building. The sandy wadi surface
could hide hauling tracks or even walls built to control flash floods.
The eastern end of the wadi may have emptied into an ancient harbor which
could have extended from an area to the east of the Khafre Pyramid Valley
Temple, up along the eastern edge of the Menkaure Pyramid Valley Temple,
and down along the north side of the Wall of the Crow—a distance of more than
Tremaine surveyed the eastern and western sections of the Central Wadi.
The results are shown in Figure 7. The eastern section
was largely devoid of changes in conductivity which could indicate a relatively
uniform layer of sand overlying the wadi floor. To the west, more variation
in conductivity was recorded. The L-shaped anomaly could be due to
The Sphinx, Sphinx Temple, and adjacent Khafre Valley Temple (E in Figure 2) have buried features that Dr. Zahi Hawass
is still discovering. Remote sensing could be useful in detecting these.
During excavations in 1980, Dr. Hawass found that a relatively smooth bedrock
terrace extends some 35 meters east of the Sphinx Temple. This terrace probably
runs no more than 10 or 15 meters beyond the excavated area, based on core
sampling done in 1980 by the Egyptian Institute of Underground Water and
the Ministry of Irrigation. One coring taken 50 meters east of the
Sphinx Temple revealed deposits 16 meters deep: a thick blanket of sand,
then dense, dark clay, and finally a hard surface from which the core drill
pulled up red granite.
What is visible on the surface in the area today is shown in Figure 8. Further excavations by Dr. Hawass and
Mansour Bureik revealed more of the eastern extension of two limestone ramps
at least 26 meters in length leading from a terrace in front of the Khafre
Pyramid Valley Temple eastward. Part of a group of enigmatic structures
here, the ramps slope downward, with one disappearing under more than 3 meters
of overburden at an elevation less than 14 meters above sea level.
Tunnels pass under the ramps.
In surveying the area directly to the east of the Sphinx, Tremaine found
several distinct anomalies. Number 1 in Figure
8 does not correlate with any features visible on the surface and seems
to align with the northern end of the Sphinx ditch. This could be an
ancient wall. Anomaly 2 is likely to be the remnant of a low wall which
once bordered the eastern edge of a stage built in 1969 and removed in 1996.
Number 3 is a short, linear anomaly of an unknown nature, probably a void.
Drilling and bore scope inspection may be appropriate here. The anomalies
labeled 4 are likely evidence of modern road building, perhaps pipes or cables
laid parallel to the road edge.
The Golf Course
The golf course (F on map) is twenty green, grassy hectares of archeological
terra incognita. The 9th and 18th holes lie at the very foot of the Great
Pyramid of Khufu. Thus, there is every reason to expect that features
associated with pyramid building will be found here.
Before urban Cairo encroached on this area, the golf course was part of
a sandy plain that spread out along the base of the Giza Plateau.
Today it sits approximately 18 meters above sea level. Early in the
last century this area was inundated by Nile floods. However, in ancient
times flood levels were lower. Thus it is possible that Old Kingdom
occupation could be found beneath these 20th century flood deposits.
Indeed, basalt paving stones associated with the Khufu Pyramid Valley Temple
were found reportedly more than 2 meters below the alluvial layer in sewage
trenches dug by the British American consortium AMBRIC in the late 1980s.
Geophysically, the golf course is a difficult target. In addition
to the flood layers, the golf course has been continuously loamed, seeded,
irrigated, and landscaped. All these factors create layers of high
conductivity which can mask features below.
Tremaine’s golf course survey data are shown in Figures
9 and 10. Most of what was detected was modern,
such as the dark, linear features, which are irrigation pipes. But
the nature of the vertical feature in Figure 10 is
yet to be determined.
The areas bordered in red are places where the Tremaine device could not
go. What shows up within these rectangles are mostly artifacts of computer
processing. However, a computer derived 3-D section reveals a distinct
layer 2 to 3 meters below the surface. This is the elevation at which
the archaeological horizon from the 4th Dynasty would be expected—about 15
or 16 meters above sea level. (Fifteen meters above sea level is one
of the “bench marks” for the 4th Dynasty in this area.) By way of
comparison, the base of the Wall of the Crow is approximately 15.4 meters
above sea level and the base of the basalt pavement of the Khufu Pyramid
Valley Temple, about 14.5 meters.
Remote sensing will not take the place of intensive excavation but it
is a very useful tool. Tremaine’s work demonstrates that it can provide
a head start by locating buried features and offering clues to their nature.
We look forward to more insights when Tremaine completes its analysis.
Results from the Soccer Field
Results from Area C-1, a portion of the "Workers'
Results from Area C-2 in the Workers' Cemetery.
The areas indicated may be tombs or related structures.
The Wadi itself displays relatively uniform conductivity.
It is probably filled with a uniform bed of sand. Around its edges,
however, the ancient builders may have quarried for stone. The dotted
yellow lines demark the tracks of Tremaine's vehicle.
Surveys near the Sphinx. We detected four
distinct sets of anomalies. Anomaly 1 may be a wall which served as
an extension of the "Sphinx Ditch" which bounds the Great Sphinx on the north.
Anomaly 2 may be the remnant of a stage built in 1969 and removed in 1996.
Anomaly 3 is of an unknown nature, perhaps a void beneath the surface.
Anomaly 4 is caused by the modern road which runs through the area.
The dotted lines show where Tremaine's vehicle ran in performing the survey.
The Mena House golf course lies at the very foot
of the Great Pyramid. Tremaine's data is shown at the bottom. The
red squares denote areas that the Tremaine vehicle was unable to navigate.
Most of the features detected match the surface features and are of modern
origin. Further analysis, however, detected more. See Figure
A 3D analysis of the golf course data shows a
band of features at approximately the same elevation as the City of the
Pyramid Workers AERA has been excavating to the south. The vertical
feature may be an ancient wall.