Its exact location is unknown but is said to be 100 miles north-east of Tadmor. This is most commonly associated with the modern town of Deir; however the only ford in the region is at Suriyeh where the town is now assumed to have been. Another possible location described by Conder in Easton's Bible Dictionary of 1897, however, identifies this place with Khurbet Tafsah, some 6 miles west of Shechem; this however is unlikely. There is further suggestion that the town may be associated with Carchemish ; however this may be unlikely as the towns referenced as Europus and Amphipolis are separate and there is no other indication that the cities could be the same as Thapsacus. Another reference does suggest that the town was near "Jarablos", another name for Carchemish .
The city's identification with Carchemish is supported by its similar role. In neo-Assyrian times the city of Carchemish was the main crossing point on the Euphrates. For many centuries it had been the capital city of the major neo-Hittite kingdom in north-western Syria. Trade between east and west past through it and because of this its system of weights and measures became a standard that was later adopted by the Assyrians and referred to as the Carchemish standard. This standard in trade with Syria (known as Ebir-nari, "across the river", in cuneiform texts) continued into neo-Babylonian and Persian times as illustrated by a letter from year 9 of Kuraš/Cyrus where this standard was then known as the measure of Tapsuḫu. The continued importance of the city is the reason Eratosthenes choose Thapsakos as one of the reference points for his system of latitude and longitude.
Thapsakos' identification with Europos (the Hellenistic name of Carchemish) finds some support from a corrupt passage in Plinius' Naturalis Historia. In his description of places along the Euphrates, from source to mouth, he gives the following account of the right bank of the Euphrates between Zeugma and Sura. "And in Syria [it flows past the following] towns: Europus formerly Thapsacus, now Amphipolis, the Tent-Dwelling Arabs. Thus it continue to the place called Sura". The passage reads as if there should be a list of towns and we know from classical references that there were other towns along this strip. In addition it is known that Amphipolis was different from Europus as Stephanos of Byzantine says it was called Tourmeda by the locals. One solution is to read the town list as "Europus formerly Thapsacus, ..., [Tourmeda] now Amphipolis, ..." (where the remaining towns have fallen out of the passage).
A second classical source which supports the identification of Thapsakos with Carchemish is the 401 B.C. marching itinerary of Cyrus the Younger as given by Xenophon, in his Anabasis. Farrell has shown that the march rates support a crossing at Carchemish, then across to the Balikh and then down hat river to its junction with the Euphrates. It is the same road outlined in Isidoros of Kharax' "Parthian Stations", except that there the route started from Zeugma.
The town has also been linked with Dibse/Al-Dibsi . Further it has been linked with the town of Balis in Halab district in Syria .