Harmantepe Kalesi

Harmantepe Castle is a Byzantine defensive structure built on a small natural mound in the middle of the flat plain north of Harmantepe, in the north of Adapazarı. Sources describe it as one link in a chain of mutually visible forward outposts and watchtowers that were built along the west bank of the Sakarya River in the 12th or 13th century to guard the eastern frontier of Byzantium. The tourism brochure of the Metropolitan Municipality dates the building to the 12th century, while the Provincial Directorate of Culture and Tourism gives both centuries as possible dates. According to the Directorate, the castle is one of the best preserved of the fortresses in the Lower Sakarya basin. The structure was registered as a cultural asset requiring protection by a decision of the Bursa Regional Board for the Conservation of Cultural and Natural Assets dated 18 April 1992. The surroundings of the castle were once wetland and marsh. Canals later dug on both sides turned this land into fertile farmland, and today the castle looks like a ring of stone standing alone among ploughed fields. Its plan is elliptical, close to round, and the walls are built of local stone. The curtain walls are up to 2 metres thick and between 8 and 10 metres high depending on the section. Six towers measuring on average 5 by 5 metres are spaced along the walls. The core of the towers is a fill of rubble and lime mortar, and wooden beams were laid in a grid inside this fill to strengthen the bond. Because the beams rotted over time, their positions now appear as rows of round holes in the masonry, and this is the most striking detail of the building. The upper parts of the towers have arrow slits facing in different directions. Five round-arched entrances of different sizes open into the castle from various directions, and the main gate is on the south side. Beside the gateways you can still trace the holes into which the wooden bolts that locked the gates from the inside were slid. Although some of the gate arches and parts of the towers and walls have collapsed, a large part of the building still stands and the plan of the castle is easy to read. No brick was used in its construction, only rubble stone and lime mortar. The dating of the castle was debated for a long time. Some researchers linked it to the 6th-century canal project that also led to the building of the Justinianus Bridge. Finds from the castle, however, showed that it belonged to the line of fortresses set up west of the river against the intensifying Turkish raids. Its architecture and stonework resemble those of other castles in the region, and these features show that it dates from the Byzantine period. Also known in the sources as Ab-ı Sufi, the castle is one of the fortresses, together with Seyifler Castle to the north, that were considered important for taking the lands north of the river. The most important thing to know before visiting is this: according to the Provincial Directorate of Culture and Tourism, cleaning and excavation work has been under way at the castle since 2023 and the site is closed to visitors. For this reason, check the current situation with the provincial directorate of culture and tourism before you go, do not enter the excavation area and view the castle from outside. The castle is reached by a farm track that branches off to the left from the road between Küçük Söğütlü and Akçakamış. The last 2 kilometres or so of the road are unpaved; the Directorate says it can be reached in every season, but the Culture Portal notes that access becomes difficult in rainy weather. The castle is about 13 kilometres from the city centre, and a private car is the most practical way to get there. Because the plain is flat and open, it is easy to take in the full length of the walls in a single glance from the edge of the fields. If you get the chance to look closely, search for the beam holes at the foot of the towers and the bolt sockets beside the gates, because these details best explain how Byzantine wall building worked. The surrounding land is cultivated farmland, so do not walk onto planted fields and do not drive onto ploughed soil. It is wise to bring water and shoes that can handle mud. The castle can be visited on the same day as Seyifler Castle, which lies to the north in the direction of the river's flow, and the sources stress that the two buildings were parts of the same defensive line. Having kept most of its plan, Harmantepe offers the clearest example in the province for anyone who wants to see the Byzantine frontier defences of the Lower Sakarya on site.