Following an in-depth study and comparison of the archaeological data collected by the Italian Archaeological Mission at the Friday Mosque of Esfahan in 1970s and Islamic historical sources dealing with Esfahan, this paper aims to suggest a reconstruction of the layout of the first Abbasid mosque at Esfahan – attributed by the author to 767 – and of its first enlargement carried out a few years later. In particular, though two different models can be hypothesised for the 767 mosque, i.e. the so-called “Syrian plan” and the so-called “Arab-Iraqi plan”, some observations can be made that seem to pin down the latter as the actual prototype for the first Abbasid phase, thus revealing an influence of the Arab-Iraqi model in early Islamic Iranian architecture that was maintained in the enlarged plan of the mosque.