The area in which this weekend's ethnic clashes took place is Yoruba through and through. Sagamu, about 50km from Lagos, is a typical Yoruba town, a sprawling, bustling trading centre.

This part of Nigeria is not like the Niger Delta, a patchwork of different tribes. It the homeland of one of biggest ethnic groups in the country, and one which has a reputation for holding on tenaciously to its culture.

Yorubas nowadays may be practising Christians or Muslims, but there are still shrines to the old gods scattered around the countryside, and traditional festivals - like the festival of the Oro cult which sparked off this week's violence - are still celebrated and still taken extremely seriously.

As in many west African cults of this kind, women and outsiders are forbidden to look on its masked figures. The trouble in Sagamu reportedly began when a northern, Hausa woman was killed after seeing the night-time procession.

Established Hausa community

Although Sagamu is far from the Hausa areas of northern Nigeria, it has a resident Hausa community. All big cities normally have a distinct area, where Hausa people live, talking their own language and dressing in their own style, with their own shops and markets, and their own mosques - nearly all are Muslim.

And normally they live in reasonable harmony with their neighbours, as do southern minorities in northern cities. The outbreak of violence in Sagamu seems to have taken Nigeria completely by surprise.