Mermerkule (“Marble Tower”) is probably a Late Palaiologan fortification by the Marmara Sea. Mermerkule, probably one of, if not the very last Byzantinev construction of significance in Constantinople, was built between ca. 1402 and 1410. Situated at the southwestern end of the city Land Walls, at their junction with the Sea of Marmara, the fortified palace belonged to a series of such private residences constructed along the city walls, starting in the late twelfth century at the city’s northeastern corner. The phenomenon of fortified residences appears to have become widespread, not only on the territories of the Byzantine Empire, but also in the neighboring states of Bulgaria and Serbia during the late thirteenth and fourteenth centuries. Mermerkule was conceived as a small heavily walled-in enclosure, measuring ca. 33 × 18 m in plan. Its western side, once sitting in the waters of the Sea of Marmara, is now land bound. The eastern side of its enclosure was dismantled during the construction of a six-lane highway in the 1960s providing the main traffic access to the city from the south. Only traces of the massive southern walls have survived facilitating the sense of a fortified enclosure, whose western and southern parts are preserved essentially to their full height. The main part of the complex is a four-story massive tower, measuring ca. 10 × 10.8 m in plan and ca. 25 m high. Originally strategically located on the seafront, the tower rose from a massive, multi-stepped platform made from huge re-used marble blocks.
The tower, as well as the walls enclosing the palace, had very few small exterior windows. Most of the natural light, therefore, came into its interior spaces through large openings facing the central interior court. Especially telling are the two-storied interior arcades consisting of large arches supported on massive piers. The system of interior arcading is characterized by high-quality construction, especially distinguished by banded arches revealing a method of arch construction that became quite common in Constantinople from the last decades of the thirteenth century on. Practically nothing of the interior decoration of the palace itself survives, making the understanding of the building’s interior spaces and their intended functions almost impossible. This, of course, is a general case with most secular Byzantine buildings of which very few survive anywhere, including in Constantinople itself. Of all parts of the surviving interior spaces in the Mermerkule palace, the interiors of the main tower are of particular interest, especially its two central, superimposed rooms on the ground, and on the second floor. The ground-floor room was vaulted by a pendentive brick dome, 4m in diameter, while its side walls forming a square, 4 × 4 m in plan, expanded laterally into deep barrel-vaulted niches. A similar scheme was repeated on the second floor, though the condition of its dome and side vaulting is not as well preserved. Only the east and north exterior walls of the top two floors survive. The exact function of either of the two lower rooms is not known, but they must have been spaces of special importance on account of their central position, their size, and the fact that they were both domed. Ceremonial functions, undoubtedly, must have taken place in this part of the palace. Use of domical vaulting, and especially of domes in towers of this size and type were fairly rare in Byzantine architecture, and appear mostly in buildings of special significance in secular contexts.
Bildlexikon zur Topographie Istanbuls: Byzantion, Konstantinupolis, Istanbul by Müller-Wiener
The Bazaar in the Islamic City: Design, Culture, and History edited by M. Gharipour