Between the eleventh and the fourteenth century Asia Minor, which was part of the Christian Byzantine Empire, came under Muslim rule. My dissertation argues that the most profound transformation brought about by the Islamic conquests was economic, and not religious. As a result of a dramatic shift in patterns of communications and trade connections, this region, which for over a thousand years belonged to Mediterranean polities, became incorporated into Greater Iran. As a western frontier of the Iranian world Asia Minor was now a land of opportunities that attracted migration and investment. Intensification of trade, the rise in agricultural productivity and diversification of regional economy created ideal conditions for urbanization. The rise of cities was the most remarkable feature of the medieval transformation of Asia Minor, completely overlooked by historians focusing on religious change. By offering this revision my research will help scholars reinterpret the history of cultural contact and conflict in frontier regions throughout the medieval world. I examine the above transformations through a case study of north-central Asia Minor. I use written sources combined with archaeological and environmental data to write an economic and environmental history. My written sources include chronicles, letter collections, sermons, biographical dictionaries, and inscriptions in Greek, Armenian, Persian, Arabic and Turkish. In addition to this, I use archaeological evidence from the medieval excavation site of Komana (Tokat), as well as coins and seals from the collections of multiple provincial museums. From September 2016 until August 2017 I will conduct research in the Turkish cities of Amasya, Niksar, Tokat and Sivas, as well Ankara.