This mosque was built in 1339, just 13 years after the conquest of the city by the Orhan, son of Osman who captured Bursa and made it the first Ottoman capital. The mosque has been repeatedly restored. It has a T-form ground plan.

On the picture: Standing in front of the mihrab (prayer niche) and looking towards the north, where the entrance is. The T-form ground plan of the congregation hall of early-Ottoman mosques (the so-called ‘Bursa-type’ mosques) is derived from the late-Seljuk medrese-with-covered-courtyard, with three large iwans (half-open rooms) opening upon a central space. In this mosque, these four rooms are still distinct from each other: their floors are not on the same level.
As the first Ottoman rulers (at least up to their conquest of Constantinople) had strong ties with various Sufi Orders, it is clear that the Bursa-type mosques were designed as multi-functional buildings to meet the needs of these brotherhoods: a place to worship (the ‘mihrab’-room), but also to teach and debate (the ‘iwan’-rooms on the left and right) and even to stay overnight (for this purpose, the Orhan Camii has two smaller rooms on both sides of the vestibule).

Correspondent: J.M.Criel, Antwerpen.
Sources: ‘Vakıf Abideler ve eski Eserler (volume III)’ - Vakıflar Genel Müdürlüğü, Ankara 1983 , Wikipedia
‘Encyclopedia of the Ottoman Empire’ - Gábor Ágoston & ‎Bruce Alan Masters, 2009
& Website of ‘nkfu.com’ .