Architecture

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 meters 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 the 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 the 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 at the center, flanked by crosses and lattices, possibly serving as the Kantakouzenos monogram.

The 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.