Ulu Mosque located on the northern hillside of the Spil Mountain was built between the years of 1366-1368 by İshak Çelebi, the grandson of Saruhan Bey. It was built in place of an old church by using some old architectural pieces. Wood engraved pulpit door is in the ethnography section of Manisa Museum. The Fethiye Madrasah in the west of the mosque which was one of the important structures of the city in the 14th and 15th centuries was built by İshak Çelebi in 1378. İshak Çelebi and his family are buried in the tomb at the madrasah