Sardis, Church M

The Church M at Sardis near the southeast corner of  the Temple of Artemisis in fact a small chapel erected in the fourth century. Originally the rectangular nave and a semicircular apse. Interior was illuminated by small windows in the upper walls. The small doors led to the northern chamber of which only foundations remained. Later apse has been enlarged and equipped with a wide arched window.  It was discovered in the early 1900s by renowned professor of Art and Archaeology at Princeton, Howard Crosby Butler (1872-1922) on the First Sardis Expedition. 

See:

1. https://www.bibleplaces.com/sardis/