This is the Muradiye mosque, by the greatest Turkish architect, Sinan. It is one of his last works, from 1582-1585, who built it for Murat III.

The mihrab (prayer niche, directed towards Mecca).

The mihrab is surrounded by tiled walls (Iznik tiles, late 16th century) of the best quality.
A particular feature of this mihrab are the two slender colonettes in brown marble on both sides of the niche. They are inserted loosely into their place, so that they can rotate around their axe if one tries to make them do so. This is more than a fiddling: it is an earthquake alarm. The endless history of earthquakes in Anatolia learned that large crowds gathering in covered spaces is potentially life-threatening. If an earthquake is imminent, the preliminary vibrations will make the pillars rattle, a warning to the attendees that it would be wise to interrupt the prayer and go outside before seeking Allah’s protection any futher.

Correspondent: J.M.Criel, Antwerpen.
Source: Personal visits (1986 – 1990 – 1998).