Encompasses both secular and religious styles, the design and style made by Muslims and their construction of buildings and structures in Islamic culture included the architectural types: the Mosque, the Tomb, the Palace and the Fort. Perhaps the most important expression of Islamic art is architecture, particularly that of the mosque. Through Islamic architecture, effects of varying cultures within Islamic civilization can be illustrated. Generally, the use of Islamic geometric patterns and foliage based arabesques were striking. There was also the use of decorative calligraphy instead of pictures which were haram (forbidden) in mosque architecture. Note that in secular architecture, human and animal representation was indeed present.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): What is considered the most important work of Islamic architecture?
the mosque