Town Walls and Earthworks

The most impressive physical remains of pre-colonial Yorubaland are not buildings. They are holes in the ground and the banks thrown up beside them, and they are enormous. Sungbo's Eredo around the Ìjẹ̀bú kingdom runs over a hundred and sixty kilometres and reaches twenty metres from the bottom of the ditch to the top of the bank; Ọ̀yọ́-Ilé had five wall circuits enclosing about fifty square kilometres; Ilé-Ifẹ̀ has an outer ditch of sixteen kilometres enclosing over two hundred square kilometres.

These are not decorative. They are the physical record of what a Yoruba polity could command in labour, and they are the strongest available evidence, independent of any oral tradition, for the scale of political organisation in the region and when it existed.

The technique

The construction method throughout is bank and ditch. Earth is excavated from a ditch on the outside and thrown up into a rampart on the inside, so that the effective obstacle an attacker faces is the ditch depth plus the bank height, and the excavated material is used rather than carted. Where the ditch is cut into laterite it stands with near-vertical faces, and this is why Sungbo's Eredo is described as having unusually smooth walls 1.

The advantages are that the technique needs no stone, no mortar and no specialist trades, only organised labour and time, and it works in forest and savanna alike. The cost is maintenance: an unmaintained ditch silts and an unmaintained bank slumps, which is why the surviving circuits are often visible as shallow features that give no impression of their original scale.

Sungbo's Eredo

Extent. Over one hundred and sixty kilometres in total length, forming an uneven ring around the ancient Ìjẹ̀bú kingdom, with the height difference between the bottom of the ditch and the upper rim of the inner bank reaching twenty metres 1. It represents an estimated three and a half million cubic metres of moved earth and sand 2. Some sections are only about eight metres wide 1. Ìjẹ̀bú-Òde sits inside the enclosure 2.

Dating, which is contested. This should be reported as unresolved because it is. Carbon dating extends back to 2000 BCE, which does not necessarily indicate that the ditch was constructed then; Patrick Darling proposed the tenth to eleventh centuries; more recent excavation suggests the end of the fourteenth and the beginning of the fifteenth century; and the widely cited range of 800 to 1000 CE appears in the reference literature on the Ìjẹ̀bú kingdom 12.

The spread matters. A tenth-century date makes the Eredo evidence of large-scale organisation in the Ìjẹ̀bú area centuries before the Ọbanta dynastic tradition, which places the founding dynasty in the fifteenth century, and therefore implies that Ọbanta represents a dynastic arrival into an existing polity. A fifteenth-century date makes it roughly contemporary with that tradition and removes the implication. Which is right is not settled, and any account that presents one date as established is overstating the evidence.

Survey. Measurements of the whole earthwork were completed in 1998 by the British archaeologist Patrick Darling, mapping previously unknown sections covered by centuries of forest growth, and he surveyed the site in September 1999 and began publicising a bid to preserve it and raise its profile 1. Darling claimed the Eredo is the largest single monument in Africa by sheer bulk, exceeding the Egyptian pyramids 1. Take that as his claim, made in the course of a preservation campaign, rather than as a settled comparative finding; the underlying volume figure is not in dispute.

Recent work. In 2024 Augustine University Ilara partnered with researchers from William and Mary to conduct LiDAR mapping of the site 13. LiDAR is the appropriate technology here because it strips vegetation from the surface model and reveals earthworks under forest canopy, and it is the method that has transformed the study of comparable features elsewhere.

The tradition. Ìjẹ̀bú tradition associates the earthwork with Bilikisu Sungbo, a wealthy childless widow, and communities hold that her grave is at Ọ̀kè-Èrì north of the site, where Christians and Muslims attend an annual pilgrimage together 1. Some pilgrims identify her with the Queen of Sheba. That identification has no historical basis and should be reported as a devotional tradition rather than a claim about the past. What the tradition does record, and record accurately, is that the works were commissioned by a single authority and were understood to be a woman's.

The Ọ̀yọ́-Ilé circuits

Ọ̀yọ́-Ilé has three principal documented concentric circuits: an inner wall enclosing the ààfin at 7.5 kilometres circumference, a main outer wall at eighteen kilometres and an outermost wall at twenty-eight kilometres 4. A wider survey identifies five wall systems in total, built between the sixteenth and the late eighteenth centuries and spanning about fifty square kilometres 5. An account of 1829 describes the walls as about twenty feet high with accompanying ditches 4.

Five circuits over two centuries is a record of repeated expansion. Each new wall marks a moment at which the city outgrew the one before, which makes the wall sequence a growth curve for the imperial capital.

The Ifẹ̀ ditches

Ilé-Ifẹ̀ has an inner bank-and-ditch system of approximately seven kilometres circumference and an outer ditch of sixteen kilometres, the latter enclosing over two hundred square kilometres 6.

The dating is the interesting part and it is counterintuitive. The Ifẹ̀ outer system is dated to the mid-nineteenth century, in the reign of Ọ̀ọ̀ni Abẹ̀wẹ́ilà, 1848 or 1849 6. That is to say the largest Ifẹ̀ earthwork is not a monument of the classical period at all but a response to the nineteenth-century wars, built by a town that had been sacked by Ìbàdàn in 1859 or was anticipating being sacked.

There is a separate and older tradition of a perimeter wall at Ifẹ̀ built in the tenth to eleventh centuries and associated with Odùduwà 7, which belongs to the classical city rather than to the nineteenth century. Keep the two apart.

The Ìbàdàn wall

Parts of Ìbàdàn's defensive wall survive 8. The Ìbàdàn circuit is a nineteenth-century construction, built and rebuilt as the war camp expanded into a city of over a hundred thousand and then over two hundred thousand, and it is among the largest of the late Yoruba walls precisely because the town it enclosed was the largest.

Ìbàdàn's wall is the clearest illustration of what these works cost politically. A town whose promotion ladder ran on war could mobilise the labour for a very large circuit; a town without that structure could not. The wall records the same military organisation that the chieftaincy ladder records.

The other circuits

Ilésà measured about three kilometres across within mud-built walls and a ditch 9. Abẹ́òkúta had multiple defensive walls 5. Kétou was enclosed by a mud-brick wall pierced by a single gate, the Akaba Idena, with trenches reported at fifteen to twenty feet deep, destroyed by Dahomey in 1886 and rebuilt in 1894 10. The Ìjẹ̀bú-Òde walls were noted by a visitor in 1854 to 1855 as higher than elsewhere and buttressed on the outside 11. Ìgbòho was surrounded by triple walls, which the tradition credits with enabling the Ọ̀yọ́ to resist the Nupe from there during the interregnum 12.

The 1505 Portuguese account of a very large city called Geebuu surrounded by a great moat is the earliest written notice of any of these works, and it is a notice of the Eredo or of an inner Ìjẹ̀bú-Òde circuit 2.

What the earthworks establish

Three things, and it is worth separating them from what they do not establish.

They establish scale of labour mobilisation. Three and a half million cubic metres is not a village project. It requires an authority able to command a large workforce over a sustained period, feed it, and direct it to a single plan.

They establish duration. Circuits built in sequence over two centuries at Ọ̀yọ́-Ilé, and maintenance of the Eredo over whatever period it was maintained, indicate continuity of political authority rather than a single burst.

They establish a defensive logic that is territorial rather than merely urban. The Eredo does not enclose a town; it encloses a kingdom, and so does the Ifẹ̀ outer ditch at two hundred square kilometres. These are frontier works.

What they do not establish is which dynasty built them, or when in several important cases. The Eredo's dating spread of more than two thousand years between the outer proposals is the honest state of the evidence, and the current condition of most of these features, unprotected, unmapped except in patches, cut through by roads and settlement and quarried for earth, means the evidence is degrading faster than it is being recorded. The 2024 LiDAR project at the Eredo is the kind of work that would need to be done at Ọ̀yọ́-Ilé, Ifẹ̀ and Ìbàdàn before much more is lost.