Why did rectangular houses become more common in the western African savanna?

In the western African savanna, the architectural trend has shifted toward rectangular-plan houses primarily due to the influence of Islam spreading from the north and increased contact with rainforest peoples from the south.1

Muslim builders introduced rectilinear, flat-roofed dwellings constructed of sun-dried mud brick or mud and stone, which reflected Arab and North African traditions. As this form penetrated the Nigerian savanna by the 16th century, it gradually replaced traditional cylindrical huts, a change also linked to evolving family sizes. While cylindrical units remain common in the region, the adoption of rectangular plans—sometimes featuring molded corners—has become a significant trend throughout the western savanna.21