Kıdemli Baba Sultan was an early Bektashi dervish-saint who gathered many disciples in Thrace; tradition links him to Hacı Bektaş and Ahmed Yesevi. His domed türbe on Ada Tepe above the village of Kalugerovo, about 15 km from Nova Zagora, is one of the earliest surviving Ottoman dervish monuments in Bulgaria, dated architecturally to c. 1413–1420. The remote site was recorded by Evliya Çelebi in the 17th century and studied in detail by Machiel Kiel in 1971; it served as a Bektashi tekke center until the order's suppression in 1826/1842. (Sources: Machiel Kiel, 'A Monument of Early Ottoman Architecture in Bulgaria: The Bektaşi Tekke of Kıdemli Baba Sultan', Belleten 35/137, 1971; Evliya Çelebi, Seyahatnâme.)