Ottoman conquest of İstanbul (Constantinople) is undeniably one of the most influential events in the World's History. This book sheds light into a fortress which was built as a strategic military preparation of this event. Rumeli Fortress has a unique place in the history of world with Its properties. The study gives information about the castle and Fatih period, explains the aspects of the castle which is thought to be important and mentions the gradually ruined or transformed parts. The castle which may be considered as one of the most strategic military buildings of Ottoman Empire in 15th centry is explored withinn Its context by using historical research methodology presented mainly by Togan. One of the still erect physical primary evidence building of the history which is directly related with the conquest of Constantinople (İstanbul) has survived against nature, politicial and civilizational effects. The study may be considered as an ideal medium for the followers of history from a critical and sceptical point of view. In depth analysis of this building makes the study an excellent source for architecture, history and design related communities.