Mermerkule (“Marble Tower”) is a large four-story tower built of reused marble blocks once was located at the southwestern corner of Byzantine Constantinople. Originally the westernmost tower of the Marmara Sea Walls, it was part of a fortified complex with a central courtyard and its own cisterns. The complex has been associated with the palace of Theodoros Palaiologos Kantakouzenos dated to around 1402-1410, though this identification has also been rejected.
The design of the Mermerkule complex, which suggests a need for both external and internal security, is consistent with what is known about urban mobs in Constantinople. Fortified residences for protection from both internal and external attacks were likely common in Constantinople during the Late Byzantine era. The so-called Palace of the Porphyrogenitus (Tekfur Sarayı) can be compared to the palace at Nymphaion near Magnesia (modern Manisa) or even the tower house of Niketiaton Castle (modern Eskihisar) in Bithynia. The Tower of Eirene also might be the remains of a fortified palace in the city associated with Lukas Notaras. In contrast, the Mermerkule complex has been compared to the fortified residence of Serbian despot Đurađ Branković at Smederevo in Serbia; Georgios Palaiologos Kantakouzenos was likely a key figure in its construction. Theodoros Palaiologos Kantakouzenos, the father of Georgios, is known to have built a palace around 1402-1410; it has been argued that it is the complex at Mermerkule. A cornice with monograms of Palaiologos and Kantakouzenos families has been used to support this identification.
Another known fortified residence at the Golden Gate, known as the Kastellion of Chryseia, was built around the second half of the 14th century. In 1354, at the end of a civil war, John VI Kantakouzenos (1347-1354) handed over the fortress at the Golden Gate to John V, which he had recently renovated and refortified. This fortress was rebuilt or reinforced by John V Palaiologos (1341-1391), who dismantle the Church of All Saints and Church of Forty Martyrs as well as the ruins of the Basilica of St. Mokios to use as building material. He resided in this fortress at the Golden Gate in 1390, when his grandson, John VII took control of Constantinople. Sultan Bayezid I (1389-1402) ordered John V to dismantle it in 1391, threatening to blind his son and future emperor Manuel II, who was held as an Ottoman hostage at the time. The spolia in Mermerkule could be associated with this construction phase of the area or even belong to it. Following this line of argument, the cornice with monograms of Palaiologos and Kantakouzenos families would simply be spolia, rather than belonging to the initial phase of the construction of Mermerkule.
Cornice with Palaiologan monogram
Flanked crosses and possibly monograms of Kantakouzenos
Monogram of Palaiologos
From Outer narthex of Chora
The complex is a small heavily fortified enclosure, consisting of a major tower, Mermerkule, built of marble spolia, with a curtain wall connecting it to a smaller northeaster tower. Located between the southernmost tower of the Theodosian Walls (Tower 1) and Tower 102 of the Marmara Sea Walls, the structure differs significantly from the Early Byzantine walls. The remains of the complex, a curtain wall and two towers, measure around 33x18 meters, with only traces of its southern curtain wall have survived. The area significantly changed in the second half of the 20th century, with most of the remains of the curtain walls between Mermerkule and the first tower of the Theodosian Walls being demolished for the construction of a highway in the 1950s and the coastal area being expanded by 20 meters from the original shoreline. Originally the tower was surrounded by water on three sides.
The main tower consists of large marble blocks of spolia up to its cornices around the level of the curtain wall. The tower has a plan measuring around 10x10.8 meter with a height of approximately 25 meters. It consists of four stories and a platform with a crenellated parapet rising high above the curtain walls. The tower has four arched openings in the courtyard, two on the lower floors, one at the parapet level, and final one on the fourth floor. The lowest stories are approximately 4 meters wide, with four arches niches. The inner walls of the tower consist of large limestone blocks, while its arches and vaults are made of bricks. The ceilings of each floor have brick domed vaults with crosses. There are arrow slits in the side niches of the lower floors. The upper floors have small windows on three sides, with arched stone plates above the third floor windows and stone lintels above the fourth floor windows. The northeastern tower is around 6.5 meters wide with two floors with vaulted domes. The curtain walls, approximately 3 meters thick, are made of limestone blocks, likely consisting of reused material. Above the upper cornice, the tower and the parapet have masonry that consists of three layers of small limestone blocks and three layers of brick. The arches of the inner courtyard alternate between a single limestone block and three bricks. They have two levels of casemates, which are separated by cornices. Each of the niches has an arrow slit. There is another cornice between the second level and battlements. The exterior wall has two cornices, one at the level of the floor of the lower curtain niches and thus also the courtyard, and another one at the level of the battlement floor. Most of the cornices of the curtain wall were replaced during restoration, though some of the original cornices with lotus palmette friezes have survived. It is possible they came from a domed cross-in-square church perhaps dating to the 11th or 12th century. There is another cornice fragment with monograms in the upper niche of the western curtain wall. A Palaiologan monogram is in the center, flanked crosses and lattices, possibly serving as the Kantakouzenos monogram.
Remains of four small cisterns are located in the small courtyard of Mermerkule. The two main cisterns, which were built adjacent the eastern wall of the complex, have a rectangular plan with beveled corners measuring around 5x4 meters. Part of the vaulting of the southernmost cistern (height approximately 1.7 m) has survived. The waterproof plaster of the cistern walls is 3 cm thick. The second and third cisterns are connected by a terracotta pipe, with the third cistern only partially surviving. A fourth small round cistern is located at the northeastern tower of the complex.
Cornices with lotus palmette friezes
Remains of courtyard with cisterns
Cistern in the Courtyard
Hypothetical Reconstruction of YK-12 from the Yenikapi excavations and Mermerkule by Byzantium 1200
At Istanbul University Rıdvan Çelikel Archaeological Museum
Tower 1 and Mermerkule
Josiah Wood Whymper (1875)
Sébah & Joaillier
Tower 1 and 2 by Basile Kargopoulo
From the Nicholas V. Artamonoff Collection
Insurance Map of Kazlıçeşme by Pervititch (1922)
Fortified Palace of Mermerkule
Reconstruction by Dimanić
Reconstruction Tower 1 from Krischen
Plan of Walls and Mermerkule from Peschlow
Architecture in the Balkans from Diocletian to Süleyman the Magnificent by Slobodan Ćurčić
Eastern Medieval Architecture: The Building Traditions of Byzantium and Neighboring Lands by Robert Ousterhout
Landmauer Von Konstantinopel-Istanbul: Historisch-topographische und Baugeschichtliche Untersuchungen by Neslihan Asutay-Effenberger
İstanbul Haliç Ve Marmara Surları, belgeleme Çalışmaları, Tarihi Ve Peyzaj Değerlerinin Korunmasına Yönelik Öneriler by Nisa Semiz
İstanbul'da Bizans Dönemi Sarnıçlarının Mimari Özellikleri ve Kentin Tarihsel Topografyasındaki Dağılımı by Kerim Altuğ
The Last Centuries of Byzantium, 1261-1453 by Donald Nicol
“Visible And Invisible Aspects Of Building: The Fortified Palace Of Smederevo And Its Historical Significance” by Slobodan Ćurčić
“Die befestigte Residenz von Mermerkule. Beobachtungen an einem spätbyzantinischen bau im Verteidigungssystem von Konstantinople” by Urs Peschlow
“Mermerkule-Ein spätbyzantinischer Palast in Konstantinopel” by Urs Peschlow
“Wer erbaute Mermer-Kule?” by Neslihan Asutay-Effenberger