Dirham, Abbasid caliphate, Madinat al-Salam, al-Mahdi, 778/779
This coin was struck in Madinat al-Salam (now Baghdad in Iraq) for the Abbasid caliph al-Mahdi in AD 778/779. Abbasid dirhams bear no images, just like the coins that preceded them, but they are given some new inscriptions and quotations from the Quran. From al-Mahdi onwards, the name of the caliph may appear on the reverse (back), as you can see on this coin.
The Abbasid dynasty was founded in AD 750 after the last Umayyad caliph was assassinated, and the Abbasids moved the capital of the Caliphate to Baghdad.