Early Byzantine architecture evolved from Early Christian architecture. The early Christian style typically was a basilica with three or five isles. Usually they had wooden roofs. Vaults and domes were rarely used. Byzantine architecture rarely used three isle or five isle basilicas. In this style domes were frequently used. The Semi-dome was also used, especially over an apse. It reached its highest form with the use of the pendentive. These are usually used to support a dome. The Byzantine pendentive is a geometric form using four triangular legs sitting on a square base. It developed during the 6th century reign of the Byzantine Emperor Justinian I. This is when Byzantine architecture became a distinctive style. Windowed domes were also a distinctive feature of this style. The intent was to make the dome look like a crown with jewels of light.