Sultan Mehmed II., the active role of Bursa and its qualification as the administrative center had faded away. There are no buildings surviving from the Roman and Byzantine era. It is believed that the walls surrounding the city were built by Bithynians and used by the Romans, Byzantines, and Ottomans after maintenance. Bursa had developed more than other cities in the first two centuries of Ottoman rule. It was filled with a number of architectural structures and became a trade city as well as a science city, where various famous madrasahs were located. Hüdavendigar Complex of Sultan Murat I., Yıldırım Complex of Sultan Bayezid I., and Green Complex all began their construction under Sultan Mehmed I. and were finished by Sultan Murad II. They affected the spatial development of Bursa and still exist to this day. Industrialization within the city was accelerated in the republican era, so that the population and the urban development of the city changed in the 1960s. The geographical location and the agricultural and industrial potential have increased the attraction of the city. Geography Osmangazi, the center of social and economic relations for years, is in the crossroad of roads to İzmir, İstanbul and Eskişehir. Osmangazi is the biggest district of Bursa that is on the southwest coast of Marmara Sea. Gökdere River on the east, Nilüfer River and Mudanya Road on the west, Katırlı Mountains on the north, Uludağ and Kirazlı Plateau are the natural and artificial boundaries of the district. Economy The following types of industries exist in Osmangazi: automotive supply industry, textile, towel, knitter & tricot, shoe industry, agricultural machines, furniture, leather, plastic, machine and metal industry, electric, foundry, welding machine, stove and knife sectors. Moreover, there are also oil and flour factories. Education Two vocational high schools are located in the district, Bursa Sports High School at Sevgi St. in Veysel Karani neighborhood, and Bursa Agriculture Vocational High School at Hürriyer St. in YeniKaraman neighborhood. Main sights Reşat Oyal Culture Park, which is the symbol of Bursa, İnkaya Plane which is the natural monument of 500 years old, Tophane Slopes, Kozahan, which is located between Ulu Mosque and Orhan Mosque, Emirhan which was built by Orhan Bey in 1340, Muradiye Complex which is composed of madrasah, school, soup house, bath and mosque, and more than twenty tombs including Murat II. and Cem Sultan, Hüdavendigar Mosque, Grand Mosque of Bursa, which is the