Eight huge medallions , bearing the Arabic names of Allah , Mohammed , two of his grandsons , and the first four caliphs , and a quotation from the Koran in the crown of the dome , are remnants of Haghia Sophia 's 500 years of service as an imperial mosque , as are the elaborate mihrab and mimber in the apse .
The medallions were made of bronze and copper and covered in delicate gold leaf .