ISLAMIC, 'Abbasid Caliphate. Al-Mahdi, AH 158-169 / AD 775-785. Dirham (Silver, 24 mm, 2.91 g, 12 h), citing al-Mahdi as 'al-Khalifa', Madinat al-Salam, AH 161 = AD 777/8. SICA III, 1622. Very fine.