09 June 2023
Schoch's water-erosion dating of the Sphinx enclosure remains the most inconvenient dataset in Egyptology. A re-examination of his methodology alongside early 20th-century interior surveys of the Sphinx suggests the structure may predate dynastic Egypt by several thousand years.
The Great Sphinx of Giza is, by conventional dating, approximately 4,500 years old — carved during the reign of the Fourth Dynasty pharaoh Khafre (circa 2558-2532 BCE) as a component of his funerary complex on the Giza plateau. This attribution is based primarily on three pieces of evidence: the Sphinx's proximity to Khafre's pyramid and valley temple, a stele erected between the Sphinx's paws by Thutmose IV approximately a thousand years after Khafre's reign that may contain a partial reference to Khafre's name (the relevant portion of the inscription is damaged and the reading is disputed), and the general stylistic consistency between the Sphinx's headdress and Fourth Dynasty royal iconography.
This is the evidentiary basis for one of the most consequential dating claims in archaeology. Two of the three pieces of evidence are circumstantial (proximity and style), and the third is literally broken.
I want to be clear: I am not arguing that the Sphinx was definitely not built by Khafre. I am arguing that the evidence for Khafre's authorship would not survive scrutiny in any other archaeological context. If an identical monument were found in South America and a researcher proposed dating it based on its proximity to a nearby structure, a damaged inscription that might contain a name, and the style of headwear depicted — that researcher would be asked for better evidence. At Giza, this level of evidence has been treated as settled fact for over a century, and the settlement has become a load-bearing wall in the architecture of Egyptian chronology. Questioning it does not challenge a single attribution. It challenges the structure built on top of that attribution.
Robert Schoch questioned it. The structure has not forgiven him.
Robert M. Schoch is a full-time faculty member in the College of General Studies at Boston University, where he holds the title of Associate Professor of Natural Sciences. His doctoral work at Yale University was in geology and geophysics. He is not an Egyptologist, a point his critics raise with the frequency and emphasis that suggests they consider it dispositive. I have addressed, in previous papers, the assumption that only Egyptologists are qualified to evaluate physical evidence at Egyptian sites. I will not repeat the argument here. I will note only that Schoch's training — in the analysis of rock weathering, erosion patterns, and geological dating — is directly relevant to the question he investigated, in a way that training in hieroglyphic translation and pottery typology is not.
Schoch first visited the Sphinx enclosure in 1990, at the invitation of John Anthony West, an independent researcher who had noted that the erosion patterns on the Sphinx body and enclosure walls did not match the erosion patterns on other structures of confirmed Fourth Dynasty date at Giza. West was not a geologist. He recognized that his observation required geological evaluation and sought a qualified geologist to conduct it. Schoch was that geologist.
What Schoch observed, and has subsequently documented in peer-reviewed publications, conference presentations, and two books (Voices of the Rocks, 1999, and Forgotten Civilization, 2012), can be summarized as follows:
The Sphinx sits in an enclosure — a trench carved into the bedrock of the Giza plateau from which the Sphinx body was extracted. The walls of this enclosure display a distinctive erosion pattern characterized by deep, rounded, vertical channels separated by convex ridges. The channels are undulating and sinuous, with smooth, curved profiles that penetrate deeply into the limestone surface.
This erosion profile is diagnostic. Different weathering agents produce different erosion patterns, and geologists can distinguish between them with the same reliability that a forensic pathologist can distinguish between different causes of injury on a human body.
Wind and sand erosion produces shallow, horizontal, angular features — flat surfaces with sharp edges, horizontal striations, and differential erosion that follows the horizontal bedding planes of the limestone (softer layers erode faster than harder layers, producing a stepped or layered appearance). Wind erosion is the dominant weathering agent on the Giza plateau today, and its signature is clearly visible on structures of confirmed Fourth Dynasty and later date throughout the site — the mastaba tombs, the pyramid causeways, the rock-cut tombs in the cliff faces. These structures display the expected horizontal, angular, bed-following erosion pattern consistent with approximately 4,500 years of wind and sand exposure.
Water erosion — specifically, precipitation-induced surface runoff — produces the vertical, rounded, deeply channeled profile observed on the Sphinx enclosure walls. Rainwater running down a vertical or near-vertical limestone surface follows gravity, carving vertical channels that deepen over time. The channels are rounded because water dissolves limestone uniformly at the contact surface (a chemical process — dissolution — rather than the mechanical abrasion of wind-blown sand). The undulating profile results from variations in water flow volume and from the natural tendency of water to find and enlarge existing weaknesses in the rock.
Schoch's central observation is that the Sphinx enclosure walls display water-erosion profiles that are fundamentally different from — and inconsistent with — the wind-erosion profiles on every other structure of confirmed Fourth Dynasty date at Giza. The Sphinx enclosure looks like it was exposed to prolonged, heavy rainfall. Nothing else on the plateau looks like this.
The significance of this observation depends on the climatic history of the Giza region. If the Giza plateau has experienced significant rainfall during the period since the Fourth Dynasty (the last 4,500 years), then the water-erosion profile could have been produced within the conventional timeline. If it has not, then the erosion predates the Fourth Dynasty and the enclosure — and therefore the Sphinx — is older than conventionally dated.
The paleoclimatic data is unambiguous on this point. The Giza region transitioned from a relatively wet climate to the current hyper-arid conditions during the late Holocene. The most recent period of sustained, heavy rainfall in the region — the Nabtian Pluvial, sometimes referred to as the African Humid Period or the Holocene Climatic Optimum — ended approximately 5,000 to 7,000 years ago, depending on the specific proxy record and geographic location. Some researchers place the effective end of regular heavy precipitation at Giza as early as 5000 BCE; others extend it to 3000 BCE with declining intensity.
Even using the most generous end date (3000 BCE), the Nabtian Pluvial ended approximately 500 years before the conventional date of the Sphinx's construction under Khafre. Using the more commonly cited end dates (5000-4000 BCE), the wet period ended one to two thousand years before Khafre's reign.
The water erosion on the Sphinx enclosure was produced by rainfall that, according to the paleoclimatic record, had ceased before the structure was supposedly built.
Schoch's conclusion: the original excavation of the Sphinx enclosure occurred during or before the Nabtian Pluvial — at minimum circa 5000 BCE, and potentially as early as 9000-10000 BCE, depending on the rainfall intensity required to produce the observed erosion depth. His most commonly cited estimate places the initial carving at approximately 7000-5000 BCE, with the acknowledgment that earlier dates are possible.
Schoch first presented his findings at the annual meeting of the Geological Society of America (GSA) in 1991. The presentation was well-received by the geologists in attendance — several senior geologists who examined the data expressed agreement with Schoch's weathering analysis and noted that the erosion patterns were consistent with prolonged water exposure. The GSA presentation was covered by major media outlets, bringing the Sphinx water-erosion hypothesis to broad public attention.
The Egyptological response was immediate, hostile, and — I must note — almost entirely non-geological.
The primary objections have been:
The Lehner-Hawass objection (subsurface water): Mark Lehner, the foremost American Sphinx researcher, and Zahi Hawass, then director of the Giza plateau, proposed that the erosion was caused not by surface rainfall but by subsurface water migration — capillary action drawing moisture from the water table upward through the limestone, causing chemical weathering from within. Schoch's response, supported by other geologists, is that capillary moisture produces a different erosion signature: efflorescence (salt crystallization on the surface), spalling (flaking of surface layers), and differential erosion following the bedding planes — horizontal, not vertical. The deep vertical channels on the Sphinx enclosure walls are inconsistent with rising moisture and consistent with descending surface water. The profiles are geologically distinct, and no example of capillary action producing the deep vertical channeling observed on the Sphinx enclosure has been documented at any comparable site.
The Reader objection (surface runoff concentration): Colin Reader, a British geologist who has studied the Giza plateau, proposed a partial compromise: that the Sphinx enclosure is older than the Fourth Dynasty but not by as much as Schoch suggests. Reader argues that the enclosure's low position on the plateau made it a natural catchment for whatever limited rainfall occurred in the early dynastic period, concentrating surface runoff into the enclosure and producing erosion disproportionate to the actual rainfall amount. Reader dates the enclosure to the Early Dynastic period (circa 3000-2700 BCE) rather than the pre-dynastic dates Schoch proposes.
Reader's analysis is the most geologically sophisticated critique of Schoch's dating, and Schoch has acknowledged it as a serious contribution. However, Reader's model still requires that the Sphinx enclosure predate the Fourth Dynasty by several centuries — an admission that, while less dramatic than Schoch's full dating range, is nonetheless devastating to the Khafre attribution. A Sphinx carved in the Early Dynastic period was not carved by Khafre. Reader's compromise, intended to moderate Schoch's conclusions, actually concedes the central point: the conventional dating is wrong.
The Gauri objection (chemical weathering): K. Lal Gauri, a limestone conservation specialist, argued that the Sphinx erosion patterns could be explained by chemical weathering processes (particularly the dissolution of limestone by moisture in the air and by dew) acting over the conventional 4,500-year timeframe without requiring heavy rainfall. Schoch and others have responded that chemical weathering from atmospheric moisture and dew produces surface dissolution — a general smoothing and rounding of features — rather than the deep vertical channeling observed on the enclosure walls. The channels on the Sphinx enclosure are centimeters to tens of centimeters deep. Atmospheric moisture does not carve channels.
I have read each of these critiques carefully. They are presented by serious researchers working in good faith. What I note is that none of them refute the fundamental observation: that the erosion profile on the Sphinx enclosure is qualitatively different from the erosion profile on every other structure of confirmed Fourth Dynasty date at Giza. They propose alternative mechanisms to explain the anomalous erosion within the conventional timeline. In each case, the proposed mechanism produces an erosion signature that does not match what is actually observed on the enclosure walls. The critique addresses the conclusion while failing to account for the data.
I want to introduce a body of evidence that receives less attention than the surface erosion but which I find equally compelling: the early twentieth-century surveys of the Sphinx's interior structure.
In 1925-1926, the French engineer Emile Baraize conducted an extensive restoration and excavation of the Sphinx, the first comprehensive modern clearing of the monument. As part of this work, Baraize documented a network of passages and chambers within and beneath the Sphinx body — features that had been noted by earlier observers but never systematically surveyed.
Baraize's survey identified:
A passage entering from the north side of the Sphinx, extending downward into the bedrock beneath the body. A chamber accessible from the rump of the Sphinx, partially natural and partially modified. A vertical shaft on the top of the Sphinx's head, cut through the bedrock to a depth of several meters. Various smaller cavities and fissures, some natural (dissolution features in the limestone) and some apparently modified by human activity.
The Baraize documentation — including photographs, drawings, and written descriptions — is archived at the Institut français d'archéologie orientale in Cairo. It has not been widely published or analyzed. Much of the modern literature on the Sphinx treats the interior features as either natural geological formations or later modifications, without engaging with Baraize's documentation in detail.
I have examined published portions of the Baraize archive, and I note the following:
The passages and chambers that Baraize documented show tool marks consistent with pre-dynastic or early-dynastic stoneworking technology — broader, less precise than the fine chisel work characteristic of Fourth Dynasty craftsmanship at Giza. This is a relative dating indicator, not an absolute one, but it suggests that the internal modification of the Sphinx body occurred before the period of peak construction precision associated with the pyramid builders.
The vertical shaft in the head is particularly interesting. It is too narrow to have served as a passage and too precisely cut to be a natural feature. Its function is unknown. Baraize documented it. Subsequent researchers have not, to my knowledge, investigated it further. The shaft connects the top of the Sphinx's head to the interior of the body — a connection whose purpose is opaque within the funerary monument interpretation but which invites speculation within other interpretive frameworks.
I also note, with reference to my earlier paper on the Hall of Records hypothesis, that the geophysical surveys conducted between 1977 and 1996 identified subsurface anomalies in the immediate vicinity of the Sphinx — anomalies consistent with constructed chambers — at locations and depths that are compatible with what Baraize documented from the interior. The geophysical data and the Baraize interior survey, when overlaid, suggest a more extensive subterranean complex than has been acknowledged in the mainstream literature.
There is one feature of the Sphinx that is visible to any tourist and that, in my view, constitutes evidence as compelling as the erosion data, though of a different kind.
The head of the Sphinx is disproportionately small relative to its body.
This has been noted by virtually every researcher who has studied the monument, including those who support the conventional Khafre dating. The head-to-body ratio of the Sphinx is inconsistent with the proportional canons observed in every other known example of Egyptian royal sculpture. The body is massive — approximately 73 meters long and 20 meters high. The head, even accounting for erosion and damage, is undersized relative to these dimensions. It looks, frankly, like a smaller head on a larger body.
The conventional explanation is that the disproportionality results from the geology of the site — that the limestone stratum from which the head was carved was harder and less amenable to carving at a larger scale. This explanation is geologically questionable (the head is carved from the Mokattam Formation member III, which is not notably harder than the underlying strata) and aesthetically unpersuasive (Egyptian sculptors, whose mastery of proportion is documented across thousands of surviving works, would not have accepted a visibly disproportionate head-to-body ratio in a royal monument unless constrained by factors more significant than rock hardness).
An alternative explanation: the head was recarved. The original head — whatever it depicted — was larger. At some point, possibly during the Fourth Dynasty, the head was recarved into a smaller pharaonic portrait (Khafre's, according to the conventional attribution) using the existing stone of the original larger head. Recarving necessarily reduces the dimensions of the carved element. A larger original head, recarved into a smaller pharaonic portrait, would produce exactly the disproportionality we observe.
This hypothesis is not new. It was proposed by West and has been discussed by Schoch and others. It is consistent with the geological evidence (the head shows less surface weathering than the body, suggesting that it was resurfaced more recently — i.e., recarved — while the body retained its original, older surface) and with the disproportionality (a recarved head is inevitably smaller than the original).
If the head was recarved in the Fourth Dynasty from a larger original, then the body predates the Fourth Dynasty. The recarving would represent Khafre not building the Sphinx but appropriating it — claiming an older monument by putting his face on it. This is not an unusual practice in Egyptian history. Pharaonic appropriation of earlier monuments is extensively documented. Ramesses II, in particular, was notorious for recarving the faces and cartouches of earlier pharaohs' statues with his own. The practice was so common that Egyptologists have a term for it: usurpation.
If Khafre usurped the Sphinx rather than building it, the conventional dating collapses — and the Sphinx becomes an artifact of a pre-dynastic building tradition whose other products we may not have recognized.
I have now written three papers that touch on the Giza plateau — the structural analysis of the Great Pyramid, the Hall of Records hypothesis, and this examination of the Sphinx. I want to step back and consider what these analyses, taken together, require of us.
They require us to accept the possibility that the Giza plateau was not a blank canvas in the Fourth Dynasty. That the pyramid builders did not arrive at an empty site and create everything we see from scratch. That some of what exists at Giza — at minimum the Sphinx and its enclosure, possibly the subsurface features identified by geophysical survey, potentially elements of the pyramid complex itself — predates the dynastic period and belongs to a building tradition that we have not identified because we have attributed its products to later builders.
This is not an outlandish proposition. The archaeological record of Egypt includes pre-dynastic structures of significant sophistication. The Nabta Playa stone circle in the Western Desert, dated to approximately 5000-4000 BCE, demonstrates that pre-dynastic populations in the region were capable of astronomical alignment and megalithic construction. The step from Nabta Playa to a pre-dynastic Sphinx is a step of scale, not of kind.
What it requires is a willingness to reexamine the assumption that the Fourth Dynasty represents the beginning of monumental construction at Giza rather than a continuation of a tradition that was already old. The erosion data suggests this. The head disproportionality suggests this. The subsurface anomalies suggest this. The interior features documented by Baraize suggest this.
I have written, in my paper on Gobekli Tepe, about the discovery that monumental construction predates agriculture in southeastern Turkey by one to two thousand years — an inversion of the standard developmental model. The Sphinx may represent a similar inversion on the Giza plateau: a monument that predates the civilization we have credited with building it.
The geological evidence has been available since 1991. It has been presented at professional conferences, published in peer-reviewed venues, and debated by qualified specialists. In over thirty years, no geologist has refuted Schoch's core observation — that the Sphinx enclosure shows water-erosion profiles inconsistent with Fourth Dynasty dating. The Egyptological community has proposed alternative explanations, none of which produce the erosion signature actually observed. The data stands.
What does not stand is the willingness to follow it. The Sphinx sits in its enclosure, worn by rains that stopped falling before the first pharaoh was born, wearing a face that may not be the face it was given, guarding whatever lies beneath its paws. It has waited a long time. It can wait longer.
But the questions it asks — about who built it, and when, and what else they built that we have not recognized — will not wait forever. Questions never do. They accumulate interest, and eventually, the cost of not answering exceeds the cost of answering.
That balance is shifting. I can feel it. And I suspect the Sphinx can too.
Correspondence: leh [at] 442423N1042233W.com
Note: Robert Schoch's geological analysis has been presented in multiple peer-reviewed venues, including the Geological Society of America's annual meeting proceedings. His book Forgotten Civilization (Inner Traditions, 2012) provides the most comprehensive published account. John Anthony West's Serpent in the Sky (Julian Press, 1993) remains the most readable introduction to the broader context, though West was not a geologist and his conclusions should be evaluated accordingly. The Baraize archive materials referenced in this paper are held at the Institut français d'archéologie orientale, Cairo.