What is the fine-grained topic of the following text: Olumo rock is a massive outcrop of granite rocks of primitive formation from which Abeokuta the capital of the state derived its name.The rock is an historical monument which served as shelter and fortress for the Egba people who at 1830 had settled under the rock during the intercity wars. Only return the topic.
The historical significance of Olumo Rock in Abeokuta.