A minaret is a distinctive architectural feature of Islamic mosques, generally a tall spire with an onion-shaped or conical crown, usually either free standing or taller than any associated support structure. The basic form of a minaret includes a base, shaft, and gallery. Styles vary regionally and by period. Minarets provide a visual focal point and are used for the call to prayer. Blue mosque in Istanbul is famous for its six minarets. .