Durusu or Terkos (Greek: Δέρκος, Derkos; also Δέλκη Delke, Δέλκος Delkos, and Δέρκοι Derkoi)[1] is a neighbourhood in the municipality and district of Arnavutköy, Istanbul Province, Turkey.
The village is attested since Classical Antiquity as Derkos/Delkos/Derkoi, but Emperor Anastasius I (r. 491–518) raised it to the status of a city and rebuilt it as a forward stronghold for the defence of Constantinople.
The moats and earthworks erected by the Ottomans during this operation were allegedly still visible in the 1660s, when the traveller Evliya Çelebi visited the city.
[1] A church dedicated to St. George still existed until the early 20th century, but today few Byzantine and ancient remains are visible; some Roman-era inscriptions are located in the Archaeological Museum of Istanbul.
[1] The medieval fortress still exists in a partially well-preserved state, some 1 km west of the settlement, close to the lake, although large sections were torn down in the late 20th century to furnish building material.