The Selimiye Mosque was built between 1801 and 1805 as the devotional centerpiece of a külliye — a charitable complex — that also included a primary school, a timekeeper's house, a fountain, a hamam, and something genuinely novel: an array of factories, shops, and a printing house arranged on a regular street grid to form the nucleus of a new neighborhood. This was urban planning in the service of modernization. Selim wanted the mosque complex not just as a place of worship but as a generator of the kind of rational, productive city life his reforms were trying to create.

Three men served as chief court architects during construction, though scholars believe the main designer was Foti Kalfa, a Christian master carpenter — an unusual choice that itself reflects something of the reform spirit. The minarets were rebuilt in 1822. During the First World War, British forces bombed the area around the mosque.

The mosque is built in the Ottoman Baroque style that defined sacred architecture in Istanbul through the eighteenth century, and it shows that style at a high point of refinement. The exterior is distinguished by Baroque stone mouldings along every edge, sculpted keystones over its arches, and — one of the period's charming signatures — small ornate birdhouses carved in stone on the corner turrets.

The most striking architectural feature is the imperial pavilion stretching across the mosque's front façade. Earlier mosques gave their sultans a loge inside the prayer hall, often a screened balcony; here, the pavilion is a multi-story structure in its own right, with two wings raised on a marble arcade, containing rooms and halls that functioned as a kind of portable palace. Between the wings, a staircase and entrance portico create a suitably grand approach. The Ionic capitals on the arcade columns, the Baroque mihrab and minbar carved in rich marble — every detail signals a building trying to be both Ottoman and cosmopolitan at once.

Step inside the prayer hall and the Baroque ambition becomes most apparent. The dome rises on pendentives, its single large span uncomplicated by the half-domes and lateral galleries that characterized classical Ottoman mosques. Those side galleries have been moved entirely outside the prayer hall, running along the exterior of the building — a decision that leaves the interior unusually open and unencumbered, the space belonging entirely to the dome above and the congregation below.

A long inscription in gold lettering on a black background runs as a band around most of the hall, in the manner of the earlier Nuruosmaniye Mosque. It contains the Surah al-Fath — the Quranic chapter of 'victory.' Whatever the painted decoration looks like today (it has been repainted in an anachronistic classical style and is not original), the inscription remains.

The complex's bathhouse, the Selimiye Hamamı, once served both mosque visitors and soldiers from the adjacent barracks. Over the decades following the empire's collapse, it fell into decay. Restoration work began in 2018, and in 2021 the hamam reopened to the public — converted to house a library, a restaurant, and a small museum area. The classroom that once educated students in the original külliye now serves as a reading room.

The barracks next door have fared less elegantly; they remain a working military headquarters, largely closed to the public. But the mosque Selim III built to sanctify them is accessible, and still holds the form he gave it — the Baroque curves and gold inscriptions of a sultan trying, in the first years of the nineteenth century, to build his way into a new era.