Special restrictions were imposed concerning the construction, the renovation, the size and the usage of the bells in churches. For example, in a town a church should not be larger in size than the largest mosque. Some churches were destroyed (e.g. the Church of the Holy Apostles), many were converted into mosques (among them the Hagia Sophia and Chora Church in Constantinople, the Rotunda and Hagios Demetrios in Thessaloniki) or served for other uses (e.g. Hagia Irene in Constantinople, which became an armory for the Janissaries, and the Gül Mosque (Hagia Theodosia or Christ Euergetes), also in Constantinople, which after the Conquest served for a while as a naval dockyard). Must also be pointed out that such rules, very strict in the beginning, with time and the increasing importance reached in the Ottoman Empire by the Rûm Millet, were more and more disregarded, so that in the 19th century in Istanbul there was a veritable building boom of Orthodox churches, many among them having high bell towers and brick domes, which previously were both strictly prohibited.
