Seleucia at the Zeugma (Greek: Σελεύκεια ἐπὶ τοῦ Ζεύγματος, transliterated Seleukeia epi tou Zeugmatos) was a Hellenistic fortified town in the present Republic of Turkey on the left (south) bank of the Euphrates, across from ancient Samosata and not far from it.
It is mentioned in isolated incidents: Antiochus III the Great married a Pontic princess there in 221 BC; the Oxford Classical Dictionary ascribed this to Zeugma.
Pompey gave the city and its surroundings to Antiochus I Theos of Commagene; Pliny the Elder nonetheless ascribes it to Coele Syria.
The name of the city is confirmed by an inscription from Rhodes, which refers to a man "of Seleucia, of those on the Euphrates".
By the same reasoning, it cannot be either of the places called el Qantara ("bridge") which were just above, and 2 km below, modern Samsat, Turkey, before its old site was also flooded, by the Atatürk Reservoir.