Nile waterscapes facilitated the construction of the Giza pyramids during the 3rd millennium BCE

The Nile River, with its dynamic floods and migratory behavior, played a key role in shaping ancient Egyptian history (1). The pyramids of Khufu, Khafre, and Menkaure, located on the Giza Plateau, overlook the west bank of the Nile (Egypt). Built during the Fourth Dynasty (Old Kingdom 2686–2160 BCE) (2), they are one of the world’s most iconic cultural landscapes and constitute ancient engineering feats that have fascinated humanity for millennia. To edify the plateau’s pyramids, tombs, and temples, it now seems that ancient Egyptian engineers took advantage of the Nile and its annual floods (3, 4), using an ingenious system of canals and basins that formed a port complex at the foot of the Giza plateau (5, 6). The harbor complex currently lies >7 km west of the present-day Nile, but it is widely accepted that Fourth Dynasty engineers exploited a now defunct branch of the Nile (7), which flowed along the western edge of the Nile floodplain during the Egyptian Old Kingdom and that we refer to as the Khufu branch. These canals and basins had to be deep enough to accommodate shallow-draft vessels all year round. Larger cargo ships could probably only navigate during the flood season (August–October), when water levels in the Nile channel rose by ∼7 m (8, 9).

The existence of a paleo-channel, canals, and harbors is now supported by recent archaeological findings (5, 6), as well as research related to the “Lost City of the Pyramids” (the Heit el-Ghurab site) (7, 10, 11). Core drillings and subterranean engineering works for Giza’s modern urban projects have yielded stratigraphic evidence consistent with a paleo-branch of the Nile. In particular, Old Kingdom structures unearthed during these interventions offer insights into the local cultural waterscape at the time of the pyramid builders. Furthermore, the Wadi el-Jarf Papyri, discovered at a Khufu-age port on the Red Sea coast (9, 12, 13), attest to the existence of such a harbor complex, called Ro-She Khufu (“Entrance to the Lake…” or “…Basin of Khufu”). The Journal of Merer, a large corpus of these papyri, describes the transport of limestone from Toura, ∼17 km from the Giza Plateau, to the construction site of the Great Pyramid of Khufu. A striking parallel exists between the names of the basins and waterways in the papyri and the spatial organization of Giza’s Fourth Dynasty waterscape, as reconstructed by archaeologists (5).

The fluvial-port-complex hypothesis postulates that pyramid builders cut through the western levee of the Khufu branch of the Nile and dredged basins down to river depth in order to harness the annual 7-m rise of the flood like a hydraulic lift, bringing the higher water levels to the base of the Giza plateau (5, 6). In this way, it was possible to transport supplies and building materials directly to the pyramid complex. These canals and ports would also have been key for the longer-distance transport of materials via the Nile, facilitating transport logistics and for the continuous supply of the plateau’s diverse building projects and linking Giza with nearby cities in the Memphite region and on the delta. Nonetheless, the interactions between ancient Egyptian societies and environmental changes along the Khufu branch are complex and poorly understood. We evaluate its water levels during the last 8,000 y, with a particular focus on the Dynastic Period and the Old Kingdom, using sediment cores and long-term ecosystem dynamics. Our data shed light on previous reconstructions because environmental and historical data are more closely coupled; such resolution has never been achieved in this region. Furthermore, our sequence can be extrapolated to upstream and downstream areas of the Egyptian Nile, allowing comparison with other archaeological sites.

To estimate variations in the water level of the Khufu branch, five cores were drilled on the present Giza floodplain, east of the pyramid complex (Fig. 1 and SI Appendix, Figs. S1 and S2). Bioindicators (pollen grains) were extracted from cores G1 and G4 (see dataset for full details) situated in what has been geographically defined as the Khufu branch of the Nile (5, 6). We identified 61 taxa (SI Appendix, Fig. S3) grouped into seven pollen-derived vegetation patterns (PdVs) based on their ecological affinities (SI Appendix, Table S1). Among the defined PdVs, the Cyperaceae (papyrus, sedge; located on the banks of the Nile), tropical Nilotic taxa (pollen carried downstream by the Nile from tropical areas of the watershed), and helophytes reveal the presence of a permanent waterbody on the Giza floodplain (SI Appendix, Table S1). The other PdVs (upland terrestrial herbs, date palm-willow, cereals, and ferns) correspond to a more terrestrial influence. We used these PdV time series (the associated dating error is averaged to ±80 y for the whole sequence) to perform a principal component analysis (PCA) (SI Appendix, Fig. S4), using PCA-Axis 1 as a proxy for Holocene Khufu-branch levels (Fig. 2). The negative values of PCA-Axis 1 are loaded by plants located on the Nile floodplain while the positive scores are weighted by taxa deriving from beyond the floodplain (SI Appendix, Fig. S4). The highest water levels are attested by high abundances of Cyperaceae and helophytes, with a higher input of tropical pollen from the Nile River, while the low levels are framed by an increase in terrestrial taxa (SI Appendix, Fig. S5). Nile flow variations, as deduced from the PCA-Axis 1, are correlated with changes in the lithofacies (SI Appendix, Fig. S6).

Our score-based reconstruction shows that the water level of the Khufu branch (termed K-1) was higher during the African Humid Period (14, 15), with a local termination estimated at 3550 ± 80 BCE (5500 ± 80 BP) and a later peak recorded at 2950 ± 80 BCE (Fig. 2) after a significant drop at 3450–3250 ± 80 BCE. During this period, it has been shown that conglomerations of predynastic and early dynastic settlements (3550–3250 BCE) existed along the east bank of the Khufu branch and on the floodplain between the paleo-channel and the pyramid plateau (16, 17). We suggest that the environmental attractivity of Giza during the fourth millennium resulted from a decrease in fluvial levels following the end of the African Humid Period (18). The reconstructed higher level of Khufu branch is also supported by Nile Delta sedimentation rates (correlation R² = 0.75, SI Appendix, Fig. S7) (19, 20), is attributed to increased rainfall over Lake Tana (correlation R² = 0.86, SI Appendix, Fig. S7), the source of the Blue Nile (21) and Lake Victoria (correlation R² = 0.84, SI Appendix, Fig. S7), the source of the White Nile (22). Nile flow is mediated by monsoon activity in tropical Africa. The Holocene intensity of the East African Monsoon, as reconstructed at Lake Abiyata (23) and Lake Rutundu (24) in Ethiopia (Fig. 3), is modulated by the north–south movement of the Intertropical Convergence Zone (ITCZ), with higher rainfall levels during the early Holocene consistent with a more northward migration of the monsoon rain belt driven by higher insolation (25). We found that the Khufu branch has recorded the same trend (Fig. 2), with a high-stand level that correlates with greater summer insolation (correlation R² = 0.88, SI Appendix, Fig. S7) and a northward migration of the ITCZ (correlation R² = 0.83, SI Appendix, Fig. S7), which reinforced the intensity of the East African Monsoon (correlation R² = 0.68, SI Appendix, Fig. S7) over the Nile Valley and created higher flow regimes in the Khufu branch (Fig. 2). The peak in the Khufu-branch level at 2950 ± 80 BCE (Fig. 2), while not documented in Lake Abiyata (Fig. 3), is recorded at Lake Rutundu, Lake Tana, and Lake Victoria, and on the Nile Delta (Figs. 2 and 3). Higher Khufu-branch levels at Giza are also in phase with higher levels in North African lakes (high and intermediate lakes; Fig. 3) (26). The most significant negative fluctuations in Khufu-branch levels during this period (∼8000–5500 y ago) are correlated with volcanic forcing (correlation R² = −0.30; SI Appendix, Fig. S7) leading to diminished Nile summer flooding (27). Moreover, a drought episode recorded in Lake Tana at 5550 BCE, due to a southward shift in the monsoon front, is also documented by a drop in the Khufu-branch level at Giza 5550 ± 80 BCE (Fig. 2).

Following the African Humid Period, the Khufu branch manifests an important and permanent drop during the Early Dynastic Period (3000–2686 BCE) as reconstructed in the core K-1 (Fig. 4). This drop is correlated with a decline in human occupation in the Eastern Sahara (28) and a slight regression of sites in Upper and Lower Egypt (28). The first dynasties of Egypt played out during a major fall in the Nile level, as attested by the Khufu branch from 2970 ± 80 to 2690 ± 80 BCE, consistent with a hydrological shift at Lake Tana (Fig. 2) and the onset of Nile Delta erosion due to decreasing sedimentation (19) (Fig. 3). This drop of the Khufu-branch level is part of long-term hydrological changes in Eastern Africa mainly triggered by orbitally driven insolation pacing as well as the variability of humid/arid periods (24, 29, 30). At Lake Abhe (Central Afar region), incursion of air moisture masses in the East African Rift System, caused by a high-pressure gradient between the Congo Air Boundary and the Indian Summer Monsoon air masses, resulted in heightened precipitation over Northeastern Africa (24). These conditions supported large waterbodies in the northern East African Rift System until ∼2650 BCE (24). At Lake Tana, the persistence of a relatively high waterbody until at least 3000 BCE probably resulted from the same conditions, even if hydrological changes in the lake have occurred since 5850 BCE. This was caused by the southward migration of the ITCZ (31), inducing a reduction in rainfall over the Ethiopian Highlands, with the lowest level of the lake recorded at 2250 BCE (21). Nile flow (Fig. 2) followed the same trend.

During the first half of the Old Kingdom of Egypt (2686–2440 BCE; Fig. 4), the level of the Khufu branch of the Nile remained relatively constant, characterized by a level at ∼40% of that reached during the African Humid Period (Fig. 2). This relatively stable phase is also recorded in North African lake levels (Fig. 3). From the third to the fifth dynasties, the Khufu branch clearly offered an environment conducive to the emergence and development of the pyramid construction site, helping builders to plan the transport of stone and materials by boat. As a consequence, the number of archaeological artifacts increased on the Giza plateau (32), particularly during the Fourth Dynasty. Between the reign of King Unas (accession date 2438–2397 BCE) (33) and the end of the Sixth Dynasty, the level (and probably the baseflow) of the Khufu branch attained its earliest low levels (Fig. 4). It has been suggested that a failure of the annual Nile flood caused severe famine episodes (34), leading to the first Intermediate Period (2160–2055 BCE). Regarding the Khufu branch at Giza, the first low point occurred at 2225 ± 80 BCE (Fig. 4), with a level that locally dropped by ∼10% compared with the Great Pyramid stage. This low level resulted from a wider-scale climatic event (35, 36) that also affected North African lake levels (26).

The Khufu branch of the Nile rose again during the Middle Kingdom (2055–1650 BCE), stabilizing throughout the Second Intermediate Period (1650–1550 BCE), before declining again (after 1350 ± 80 BCE) during the New Kingdom (1550–1069 BCE; Fig. 2). After the reign of king Tutankhamun (accession date 1349–1338 BCE) (33), the level gradually declined and reached a low value at 1075–1025 ± 80 BCE, close to the level recorded at 2225 ± 80 BCE (Fig. 2). This shift, also widely recorded in Eastern Mediterranean paleoclimatology (37), is associated in Egypt with a weaker East African Monsoon, leading to a fall in level at Lake Tana (Fig. 2) and to a strong decline of North African lake levels (Fig. 3). In 1069 BCE, Egypt transitioned into the Third Intermediate Period, which lasted for 400 y (from the 21st to 24th the dynasties) (2). While the level of the Khufu branch again increased during the 22nd dynasty, from the reign of king Sheshonq I to the reign of king Osorkon IV, the end of the Third Intermediate Period and the Late Period recorded the most important drop in Nile levels at Giza. The level is the lowest documented during the last 8,000 y (Fig. 2). This pronounced fall is correlated with an increase in δ¹⁸O values in teeth and bones from Egyptian mummies (38), suggesting a more arid environmental period (Fig. 5). A less intense East African Monsoon, low sedimentation and increased sediment losses on the Nile Delta all point to a dry phase that lasted ∼600 y. According to Bunbury and Jeffreys (39), the Khufu branch was diminished to a small channel named “Maaty” by the Middle Kingdom. The level of the Khufu branch was extremely low during the New Kingdom and when Alexander the Great conquered Egypt, at the start of the Ptolemaic Period.

The chronology from the Early Dynastic to the Late Period has been widely debated. It derives from different sources, including textual evidence, astronomical observations and ¹⁴C dating (2, 33, 40–43). Focusing on the Giza pyramids, the accession date of Khufu (Fig. 4) ranges from 2613 to 2577 BCE (1σ) according to the ¹⁴C-based chronology (33) while other sources place the onset of his reign at 2589 BCE (2), 2554 BCE (41), or 2480 ± 5 BCE based on astronomical observations (42). The same inaccuracy is noted for the reign of Khafre or Menkaure. The accession date of Khafre ranges from 2586 to 2548 BCE (1σ) (33) or is chronologically centered on 2558 BCE (2), 2522 BCE (41), or 2448 ± 5 BCE (42). The accession date of Menkaure ranges from 2564 to 2524 BCE (1σ) (33) with centers on 2532 BCE (2), 2489 BCE (41), or 2415 ± 10 BCE (42). The wide chronological ranges regarding the accession date of each king suggests that the use of the ¹⁴C chronology (33) is preferable as less subject to interpretation. This is what was used in the present study.

Our 8,000-y reconstruction of Khufu-branch levels improves understanding of fluvial landscapes at the time of the construction of the Giza Pyramid Complex, and demonstrates that Old Kingdom engineers harnessed the fluvial environment—the Nile and its annual floods—to exploit the plateau area overlooking the floodplain for monumental construction. We suggest that these paleoclimate data can also be used as a template to understand the waterscapes bordering the earlier Saqqara and Dahshur pyramid complexes, also on the West Bank of the Nile, and respectively 16 km and 22 km south of Giza.