And I saw in a vision; and it came to pass, when I saw, that I was at Shushan in the palace, which is in the province of Elam; and I saw in a vision, and I was by the river of Ulai.
When I saw ... I was at Shushan - Susa. Though then comparatively insignificant, it was destined to be capital of Persia after Cyrus' time. Therefore Daniel is transported into it, as being the capital of the kingdom signified by the two-horned ram (Nehemiah 1:1; Esther 1:2-5).
In the province of Elam - west of Persia proper, east of Babylonia, south of Media. Daniel was not present there personally, but in vision.
I was by the river of Ulai - called in Pliny Euloeus; by the Greeks, Choaspes. Now Kerah, or Karasu. So, in Daniel 4:1-37, he receives a vision near another river, the Hiddekel. So Ezekiel (Ezekiel 1:1) at the Chebar. Perhaps because synagogues used to be built near rivers, as before praying they washed their hands in the water (Rosenmuller). (Psalms 137:1.)