Seleucia on the Euphrates: Hellenistic town in ancient Iraq.
A Seleucia on the banks of the river Euphrates is mentioned in several cuneiform texts of the Hellenistic Period. The obvious interpretation is that it is Zeugma, which for a while used this name. However, this identification is impossible, although it is reasonable to assume that it was northwest of Babylon, because it is mentioned in the Ptolemy III Chronicle (BCHP 11) as a town along the road from Syria to Babylon.
The Seleucids Accessions Chronicle (BCHP 10) suggests that the city was "on the Euphrates and the Royal Canal". This make Sippar and Nehardea likely candidates, unless this is a scribal error, and in fact "Tigris and Royal Canal" is meant (and therefore, Seleucia on the Tigris).
The Astronomical Diary of 106/105 mentions the town as residence of a satrap. In that same year, according to the same source, the city's territory was attacked by Arabs. The Diary of 94/93 records that a new branch of the Royal Canal was being dug, "above Seleucia on the mountain side".
A discussion of all available sources can be found here.