The following subjects are elaborated on in this article: a) The recruitment of commanders and military units in Marw. The most important was āhir b. al-usayn and other members of his family; b) The mobilization of a non-Arab army from Khurāsān and Transoxiana; c) A discussion on the three chief commanders of al-Mamūn (and also others), āhir b. al-usayn, and two of the most honoured commanders of al-Abnā, Harthama b. Ayan and Zuhayr b. al-Musayyab b. Zuhayr; d) The armies of al-asan b. Sahl in al-Irāq from 198 or 199/813-814, which at the beginning mainly consisted of the armies of Harthama and Zuhayr b. al-Musayyab, the Abnāwīs; e) The stiff opposition to al-Mamūn and to al-Fal b. Sahl in Khurāsān.A notable opposition to al-Mamūn and al-Fal b. Sahl was that of Harthama b. Ayan and another senior Abnāwī. It seems that the main reason for this opposition, which eventually ended in Harthama’s execution in Marw, was his opposition to the murder of al-Amīn that was carried out with the agreement and approval of al-Mamūn. Close study of the evidence on the senior commanders who were sent by al-Mamūn from Marw to al-Irāq (between 200-203/815-818) reveals that most of them were in fact Arabs, or belonged to veteran families of the Abnā. Only rare information is given about the ethnic nature of their contingents; there is no evidence of non-Arab commanders or troops sent from Marw.