The muqarnas decoration of a prayer niche in the porch. There are two of them, one on each side of the entrance (and this is the left one). Their presence emphasize the porch’s function as ‘son cemaat yeri’ (= ‘area for those who came late’, where worshippers who reached the mosque late or at the last moment, will gather and fulfill their prayer duty). Such exterior prayer niches help the people here feel connected with the congregation inside.

Muqarnas is a stalactite-like decoration initiated in Anatolia by the Seljuk (in the 11th – 12th century). They imported it from Iran. Later on it continued to be used in the late-Seljuk architecture of the Beyliks (14th century) and by the Ottomans up to the 19th century.

Correspondent: J.M.Criel, Antwerpen.
Source: ‘Vakıf Abideler ve eski Eserler (volume III)’ - Vakıflar Genel Müdürlüğü, Ankara 1983 & Wikipedia.