ARZARETH är’ zə rĕth (אֶרֶץ אַחֶרֶת, another land; KJV ARSARETH, är’ se rěth). A region beyond the Euphrates River to which the Assyrians supposedly took the ten tribes after the destruction of the northern kingdom, and from which it was expected that they would return in the last days (2 Esd 13:45). The Heb. text means “another land” and is prob. not a true geographical name. The RSVmg. has “Another Land.

International Standard Bible Encyclopedia (1915)

ar’-za-reth, ar’-sareth (the King James Version, Arsareth): This is the land to which the ten tribes were deported (2 Esdras 13:45). It is described as "another land" lying a year and a half’s journey beyond the river, i.e. the Euphrates. It probably answers to the Hebrew ’erets ’achereth (De 29:28). In Josephus’ time the people were still believed to be there in countless numbers (Ant., XI, v, 2).