Abstract:
Oyo-Ile, the capital of the Old Oyo Empire located on the extreme northwest of presentday Yorubaland, Nigeria was an important polity in West Africa between the 16th and 19th
centuries A.D. The city walls, in their current conditions, are in need of restoration towards
conservation of the wall system. Previous archaeological investigations on the palace walls
had focused on their circumference, the areas covered, description of the types of walls,
and elucidation of their functions. However, limited attention has been paid to construction
techniques, the composition of materials used, and the mode of emplacement of the
artefacts found in the walls. The aim of the study was to investigate the construction
techniques, the composition of the sediment used, and the mode of emplacement of the
potsherds in the wall.
A cross-section excavation was conducted on the palace wall remains which enabled the
examination of the stratigraphy of the excavated units and the techniques used to build the
wall and its foundation, and the collection of artefacts, and sediment samples. The sediment
samples collected were subjected to granulometric analysis to determine their grain size.
The pH, exchangeable cations of the sediments were determined by standard methods and
minerals of the clay were determined from thin section. The mode of incorporation of the
potsherds into the wall was determined using pottery analysis.
Stratigraphy of the excavation showed the composition of the soil to be lateritic clay
comprising a very fine-grained gravely sand thoroughly kneaded with plant fibres. The
construction technique of the palace wall was no more traceable because the wall has been
reduced to a massive hillock. The colour characteristics of the sediments ranged from
reddish gray, yellowish red to reddish brown. The pH of the sediments ranged from 5.5-
7.5, and was consistent with the pH of the “brownearths” soil type characteristic of mixed
deciduous woodland zone within which Oyo-Ile is located. The sediment was stable and
resistant to erosion by the nature of its mineral assemblages (Quartz, Garnet, Tourmaline,
Rutile and Rock fragment) and exchange cations (K+, Na+, Ca2+, and Mg2+). The potsherds
were crude and poorly fired with thickness of 0.5-1.2 cm. The sherds were mainly
undecorated and their emplacement in the wall remains was evenly spread across the
stratigraphic layers. The features of the potsherds were not consistent with those used for
domestic, ritual or industrial purposes; rather the sherds were intentionally added to the
palace wall during construction
The palace wall at Oyo-Ile was built directly on a lateritic ground as its foundation.
However, the specific technique used to construct the palace wall could not be established.
Potsherds were deliberately mixed with the sediments to strengthen the wall.
