Seljuks continued their raids in Anatolia, which started with Chaghri Beg, during the reigns of Tughril Beg, Alp Arslan and Malik-Shah and made permanent conquests. The Seljuk raids, which especially accelerated after the Battle of Manzikert in Anatolia, were instrumental in the capture of Sinop, which was first conquered by Karatekin, one of the Seljuk commanders (1084/1085). Karatekin's rule in Sinop did not last long and the Byzantines took it back presumably in 1086. Turkey Seljuk Sultan Kaykaus I conquered Sinop in 1214, thus the city passed to the Turks again. Kaykaus I is the first Seljuk Sultan of Turkey who implemented the Turkish-Islamic culture in Sinop. The citadel inscriptions were written in this period. Both Kaykaus I, who conquered the city, and other Seljuk Sultans of Turkey attached great importance to the commercial position of Sinop. During his reign, Kayqubad I ensured the security of Sinop Port and also continued the development activities in the region. The start of Mongolian invasion of Anatolia led to extremely negative consequences for the Seljuks in Turkey, and the Empire of Trebizond dominated Sinop (1254/1259). However, the Seljuks did not give up the city and took it back again through Mu'in al-Din Sulaiman Parwana. Upon the foundation of the Empire of Nicaea following the Fourth Crusade, the Seljuk Empire of Turkey lost its connection with the Sea of Islands. As it did not have a connection to the Black Sea or to the Mediterranean either, it became a landlocked empire. Thus, they needed to reach seas. As a matter of fact, the takeover of Antalya in 1207 and 1216, and the takeover of Sinop in 1214 were critical accomplishments for them. After the reconquest of Sinop, the Seljuks of Turkey immediately spread the Turkish-Islamic culture there. The present study provides information on the policies implemented and the architectural works built by Seljuk sultans who wanted to convert Sinop into a Seljuk city. Works dating from the Turkey Seljuk era such as the Citadel, the Alaeddin Mosque, Pervane Medrese and Durakhan Caravanserai in Sinop are extant. The study also addresses the lives of certain individuals like Emir Tayboga, Cece Sultan and Sari Saltuk, who made military, religious and scientific influences on Sinop.