The Isa Bey Mosque dates from 1375, a Seljuk sultan Isa Bey I from the Aydinoðlu (son of light, or rather son of Aydin (light), not bad a name) dynasty had it built. It has a large courtyard, with a fine entrance gate, and is much more spacious than the Seljuk mosques in the East (which often are one or two centuries older).

It is a monumental example of the Damascus (Syrian) style, which is itself inspired by the early Byzantine basilica (6th – 7th century). Its surface area is 48 x 56 m large (including the yard).
In the 19th century, it has been used for some time as a caravanserai. It was restored in 1975-2005.

The Aydınoğulları Beyliği (Beylik/Principality of Aydin) was one of the Anatolian Turcoman beyliks, named after its founder Aydınoğlu Mehmed Bey. Its capital was at first in Birgi (100 km east of Izmir), and later in Ayasoluk (present day Selçuk). It was one of the frontier principalities established in the 14th century by Oğuz Turks after the decline of Sultanate of Rûm.
The Aydınoğulları also held parts of the port of Smyrna (modern İzmir) all through their rule and all of the port city with intervals. Especially during the reign of Umur Bey (mid 14th century), they were a significant naval power of the time, that played a crucial role in the Byzantine civil war of 1341–1347, where Umur allied with John VI Kantakouzenos. This provoked a Latin response in the form of the Smyrniote crusades, that captured Smyrna from the emirate.
The Beylik was incorporated into the Ottoman Empire for the first time in 1390, and after the passage of Tamerlane in Anatolia in 1402 and the ensuing period of troubles that lasted until 1425, its territories became again part of the Ottoman realm, this time definitively. The city of Aydın was named after the dynasty.

Correspondent: J.M.Criel, Antwerpen.
Sources: ‘Islamic Architecture: Ottoman Turkey’ (Godfrey Goodwin) – London 1977 & Wikipedia .