The Mosque of al-Imam Bahir, also known as Mashhad al-Imam Bahir ibn al-Husayn ibn 'Ali, was located in the old city of Mosul. The date of construction is not certain, but an inscription surviving in the tomb bears the date 1299/699 AH, providing a terminus ante quem. Whatever the original date of the monument, many changes were made to the structure over the centuries. It was rebuilt in 1940 and its significant architectural features were removed to Baghdad for preservation.
The tomb took the form of a square chamber with a conical vault. The transition from walls to vault was made with muqarnas which form an octagon.
The mihrab and portal of the original tomb were removed to the National Museum of Iraq in Baghdad during the 1940s. These elements are made of marble and richly carved with a variety of motifs. The portal consists of a square door surmounted by a lintel made of joggled stones. This aperture is framed with a series lobed niches (four on each side and four above) created by intertwining serpents. The niches are populated with vegetal motifs. Framing this is an inscription band that runs around the outside of the portal.
The mihrab takes the form of a pointed niche whose semidome articulated with muqarnas. A hanging lamp is depicted on below the semidome on the curved back wall of the niche. Framing the niche is an Arabic inscription band containing Qur'anic verses and vegetal motifs fill the spandrels of the pointed apex of the niche.
--Matthew Saba, Visual Resources Librarian for Islamic Architecture, AKDC @ MIT. May 2017 (Updated date of construction information August 2018)