A massive 2,600-year-old mudbrick complex has been discovered beneath the ancient Egyptian city of Buto, where archaeologists have also identified an engineered sand foundation that may have protected the structure from the unstable conditions of the Nile Delta.
The discovery was made at Buto, known today as Tell el-Fara'in, an ancient settlement in the northwestern Nile Delta that was one of the most important religious centres of Lower Egypt.
Researchers combined satellite radar imagery with electrical resistivity tomography (ERT) to investigate deeply buried remains beneath Kom C, one of three major mounds at the site.
The results revealed substantial architecture dating to Egypt's 26th Dynasty, or Saite period, which lasted from approximately 688 to 525 BC.
A sacred city of Lower Egypt
Buto had a long history stretching back to Egypt's Predynastic period and was closely associated with Wadjet, the cobra goddess and protector of Lower Egypt.
Although archaeologists have investigated the site for decades, its complex stratigraphy has made some of the deeper occupation levels difficult to reach.
Later Ptolemaic and Roman settlement accumulated above earlier Egyptian structures, while groundwater and waterlogged Nile Delta clay further complicated excavation.
To investigate these inaccessible layers, researchers analysed radar imagery from the European Space Agency's Sentinel-1 satellite.
The imagery revealed a large oval-shaped anomaly beneath Kom C measuring approximately 128 by 62 metres.
Researchers then conducted 15 parallel ERT surveys across approximately 5,400 square metres to map the archaeological remains below ground.
Massive Saite-period structure
The surveys revealed several distinct archaeological layers.
Within the upper three metres were scattered mudbricks, pottery and limestone fragments associated with Ptolemaic and Roman occupation.
Between approximately three and six metres below the surface, however, researchers identified substantial mudbrick architecture belonging to the Saite period.
Three-dimensional modelling revealed a large rectangular structure measuring approximately 20 by 25 metres, with substantial walls and evidence of an associated enclosure.
Its exact purpose remains uncertain.
Researchers have suggested that it could represent a tomb, religious shrine or another substantial building associated with the sacred landscape of Buto.
The Saite period represented a major resurgence of Egyptian political power and cultural activity following centuries of foreign influence and political fragmentation.
The rulers of the 26th Dynasty governed Egypt from Sais, another important city in the Nile Delta, while older religious centres such as Buto continued to hold considerable symbolic importance.
Ancient engineering beneath the walls
One of the most significant discoveries was found beneath the mudbrick architecture.
At a depth of approximately six to seven metres, geophysical surveys identified a thick layer of relatively clean sand.
Evidence from boreholes indicates that natural sand occurs considerably deeper beneath Buto, leading researchers to conclude that the shallower deposit was deliberately introduced.
The sand appears to have formed an artificial foundation beneath the Saite-period architecture.
Such a foundation could have helped distribute the weight of the structure while improving drainage and reducing the movement of the waterlogged clay beneath it.
The technique may also have helped prevent groundwater from rising directly into the mudbrick walls, which would have weakened the structure.
Study co-author Abdelaziz Elfadaly said the discovery could explain how substantial mudbrick architecture survived despite Buto's high water table and unstable clay-rich sediments.
Excavations confirm buried architecture
Researchers tested the geophysical results by excavating a 10-by-10-metre area within Kom C.
The excavation confirmed thick mudbrick walls at approximately the depths predicted by the electrical survey, providing physical evidence that the anomalies represented buried architecture.
A collection of artefacts was also recovered from the area.
Amongst the finds were ushabti and shawabti figurines (small figures placed in Egyptian burials to serve the deceased in afterlife).
They also found a limestone altar with carved channels (dried residues consistent with animal blood) which may indicate offerings were made at the site.
Another unusual find was a faience baboon figurine – an animal closely associated with Thoth the Egyptian god of wisdom, writing and knowledge.
Taken together the objects suggest that at least part of the complex was religious or funerary but further work will be necessary to determine its purpose.
Revealing what lies beneath Buto
Buto has thousands of years of archaeological deposits (the Buto-Maadi culture of the fourth millennium BC to Early Dynastic, Old Kingdom, Third Intermediate, Saite, Ptolemaic, Roman and later).
This long sequence of occupation means that earlier buildings can be several metres under later buildings and settlement debris.
The new research shows how satellite imagery and geophysical methods can reveal these inaccessible layers before archaeologists dig targeted excavations.
They now plan to carry out further electrical resistivity surveys (wider electrode spacing) so that they can investigate levels deeper beneath the site.
Studies of ancient plants and the changing geology of the Nile Delta will also be used to help reconstruct what the landscape around Buto looked like when Saite-period complex was built more than 2500 years ago.