In early times the Euphrates was important as a boundary. It was the theoretical eastern limit of the Jewish kingdom; for a long time it separated Assyria from the Khita or Hittites; it divided the eastern from the western satrapies of Persia (Ezra iv. 17; Neh. ii. 7); and it was at several periods the boundary of the Roman empire. Until the advent of the nomads from central Asia, and the devastation of Mesopotamia and the opposite Syrian shore of the river, there were many flourishing cities along its course, the ruins of which, representing all periods, still dot its banks. Samsat itself represents the ancient Samosata, the capital of the Seleucid kings of Commagene (_Kumukh_ of the Assyrian inscriptions), and here the Persian Royal Road from Sardis to Susa is supposed to have crossed the river. Below Samsat the river runs S.W. to Rum-Kaleh, or "castle of the Romans" (Armenian, _Hrhomgla_). At this point was another passage of the river, defended by the castle which gives its name to the spot, and which stands on a high hill overhanging the right bank, its base washed by an abundant stream, the Sanjeh (Gr. [Greek: Singas]), which enters the Euphrates on the west. From this point the river runs rather east of south for about 25 m. past Khalfat (ferry) to Birejik or Bir, the ancient Birtha, where it is only 110 m. from the Mediterranean, the bed of the river being 628½ ft. above that sea. This was the Apamea-Zeugma, where the high road from east to west crossed the river, and it is still one of the most frequented of all the passages into Mesopotamia, being the regular caravan route from Iskanderun and Aleppo to Urfa, Diarbekr and Mosul. From Birejik the river runs sluggishly, first a little to the east, then a little to the west of south, over a sandy or pebbly bed, past Jerablus (? _Europus, Carchemish_, the ancient Hittite capital), near which the Sajur (_Sagura_; _Sangar_ of the Assyrian inscriptions) enters from the west, to Meskene, 2 m. southward of which are the ruins of Barbalissus (Arab. _Balis_), the former port of Aleppo, now, owing to changes in the bed, some distance from the water. Six miles below this the ruins of Kal'at Dibse mark the site of the ancient Thapsacus (_Tiphsah_ of 1 Kings iv. 24), the most important passage of the middle Euphrates, where both Cyrus, on his expedition against his brother, and Alexander the Great crossed that river, and the ancient port of Syria. Here the river turns quite sharply eastward. A day's journey beyond Meskene are the remains of Siffin (Roman _Sephe_), where Moawiya defeated the caliph Ali in 657 (see CALIPHATE), and opposite this, on the west bank, a picturesque ruin called Kal'at Ja'ber (_Dausara_). A day's journey beyond this, on the Syrian side, stand the remains of ancient Sura, a frontier fortress of the Romans against the Parthians; 20 m. S. of which, inland, lie the well-preserved ruins of Reseph (Assyrian, _Resafa_ or _Rosafa_). Half a day's journey beyond Sura, on the Mesopotamian side of the river, are the extensive ruins of Haragla (_Heraclea_) and Rakka, once the capital of Harun al-Rashid (_Nicephorium_ of Alexander; _Callinicus_ of the Seleucids and Romans). Here the Belikh (_Bilechas_) joins the Euphrates, flowing southward through the biblical Aram Naharaim from Urfa (_Edessa_) and Harran (_Carrhae_); and from this point to el-Kaim four days' below Deir, the course of the river is south-easterly. Two days' journey beyond Rakka, where the Euphrates breaks through the basalt dike of el-Hamme, are two admirably preserved ruins, built of gypsum and basalt, that on the Mesopotamian side called Zelebiya (Chanuga), and that on the Syrian, much the finer of the two, Halebiya or Zenobiya, the ancient Zenobia. Twenty-six miles farther down lies the town of Deir (q.v.), where the river divides into two channels and the river valley opens out into quite extensive plains. Here the roads from Damascus, by way of Palmyra, and from Mosul, by way of the Khabur, reach the Euphrates, and here there must always have been a town of considerable commercial and strategic importance. The region is to-day covered with ruins and ruin mounds. A little below Deir the river is joined by the Khabur (_Khaboras_, Biblical _Khabor_), the frontier of the Roman empire from Diocletian's time, which rises in the Karaja Dagh, and, with its tributary, the Jaghijagh (_Mygdonius_; Arab. _Hirmas_) flows south through the land of Gozan in which Sargon settled the deported Israelites in 721 B.C. At the mouth of the Khabur stood the Roman frontier fortress of _Circesium_ (Assyrian, _Sirki_; Arab. _Kirkessie_) now el-Buseira.