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|---|---|
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| Route information | |
Part of  E90 | |
| Length | 2,057 km (1,278 mi) |
| Major junctions | |
| West end | Datça |
| East end |   Road 16 at Serow, West Azarbaijan |
| Location | |
| Country | Turkey |
| Highway system | |
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D.400 is an east–west state road in southern Turkey. The 2,057-kilometre (1,278 mi) road starts at Datça in the southwest corner of the Anatolian peninsula and ends at the Iranian border at Esendere.
D.400 runs through the cities of Marmaris, Fethiye, Antalya, Alanya, Mersin, Adana, Gaziantep, Şanlıurfa, and Hakkâri and links to Road 16 in Iran. Between Nizip and Cizre, D.400 is part of the European route E90.