text: 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 .
  
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  The medallions were made of bronze and copper and covered in delicate gold leaf .