Aydos Kalesi

Aydos Castle is a Byzantine fortress built on a spur of Aydos Hill in Sultanbeyli, 325 metres above sea level. Locals also call it Keçi Kalesi, the Goat Castle, and together with its surroundings it is protected as a first degree archaeological site. According to the municipality's information site, the castle lies about 36 kilometres east of central Istanbul and about 8 kilometres north of the Sea of Marmara. Its name comes from the Greek word Aetos, meaning eagle, and it has survived to this day with only a small change. Construction is thought to have begun in the 11th or 12th century, and later additions gave the castle its final form in the 13th and 14th centuries. Most of the remains uncovered in the excavations belong to this last phase, so these centuries are considered the period of heaviest use. The same excavations found two stone axe heads from the Early Bronze Age and many flint flakes, which show that the hill was used much earlier. In the Byzantine period the castle was an outpost guarding the trade road from Constantinople to Anatolia and the seat of the Aydos lordship that governed the surrounding land. When most of the Kocaeli Peninsula came under Ottoman rule between 1326 and 1328, the border between the two states settled on a line between Aetos and today's Pendik. According to the chronicle of Aşıkpaşazade, Orhan Gazi sent Abdurrahman Gazi, Akça Koca and Konur Alp to take the castle; the Ottoman forces first captured the Semendra castle at today's Samandıra and then besieged Aydos. In a story told by the same source and retold by many later writers, the daughter of the castle's lord helped the attackers by throwing them a letter wrapped around a stone. A miniature in the Osmanname of 1558 shows the scene with the girl letting her long braid down from the walls. The historian Halil İnalcık described the castle as "the place where the conquest of Istanbul began". Hoca Sadeddin Efendi, on the other hand, wrote that after İzmit was taken in 1337 the castle was no longer needed and Orhan Gazi had it pulled down. Covering about 26,000 square metres within its outer walls, the castle was laid out in stages, with an inner wall and an outer wall to strengthen its defence. According to the municipality's restoration page, twelve towers stand today, six on the inner wall and six on the outer one. The semicircular towers were built with lime mortar, local stone and in places brick. The largest tower, numbered 1 and holding the original castle gate, was built with a different wall technique and is therefore thought to be a later addition. This method, known in Byzantine masonry as the box technique and seen mostly in the 13th and 14th centuries, suggests that the tower was added in a later phase. Part of the stair that soldiers used to climb this tower and the remains of the platform at the top can be seen in their original state. The Sultanbeyli Municipality started excavation and restoration work in 2010; the digs were led by the Istanbul Archaeology Museums, and once the landscaping was finished the castle opened to visitors in 2022. Besides the walls and towers, the excavations revealed gates, water systems, two cisterns, living quarters and a building thought to be a grain store. The northern cistern was measured to hold about 300 cubic metres of water and the eastern one about 450. Carbonised wheat and broad beans were found in the long building to the northeast of the castle, which is why it is thought to have been the fortress's granary. The foundations of a three aisled building from the Middle Byzantine period were also uncovered inside the castle, and its marble was identified as coming from Marmara Island. A good order for a visit is to start at the entrance, go first to the great gate tower and then move towards the northern cistern and the granary remains. Thanks to its commanding position, most of the valley can be seen from beside the walls; on clear days do not forget to look towards the Marmara. Column bases, moulded stones, arch fragments and carved panels found during the excavation and restoration are displayed in the castle's presentation and exhibition hall, the Aydos Museum. The hall also shows videos on the castle's history and photographs of the twelve year restoration. According to the municipality's announcement the museum is free and closed on Mondays; check current visiting hours on the castle's official website. Do not leave the marked paths among the remains and do not climb the walls, because they are under archaeological protection. The wind on the hill is stronger than on the coast; clear days in spring and autumn are the best time both for walking and for photographs. With the M5 metro extension that opened in May 2026, Sultanbeyli is now connected to the rail network; from the Sultanbeyli and Hasanpaşa stations you can continue to the castle by bus or taxi. The Aydos Forest around the castle and Aydos Hill, the highest point on the Asian side, make a good continuation for those who want a longer day.