It is an ancient Muslim tradition to build mihrabs in Masjids. It was done during the best generations and those that followed them. It serves a public interest for Muslims, such as showing the Qiblah (Ka`bah-direction faced in Prayer) and marking the place as a Masjid. (Part No. 6; Page No. 253) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.