Watch List notes:

ABBASID: al-Ma'mun, 810-833, AR dirham (2.88g), al-Muhammadiya, AH195, A-223.3a, W-390, citing the general Tahir b. al-Husayn in the outer obverse margin, and the caliph with the title imam al-mu'minin instead of the more common variety with amir al-mu'minin, VF, RRR. Tahir received the governorship of Khorasan, with its base at Rayy (al-Muhammadiya) in honor of his masterful victory as general for al-Ma'mun against his brother al-Amin.

Estimate: 300-400 GBP