Adam Clarke on Daniel 8:2

I saw in a vision - Daniel was at this time in Shushan, which appears to have been a strong place, where the kings of Persia had their summer residence. It was the capital of the province of Elam or the Elymais; which province was most probably added to the Chaldean territories by Nebuchadnezzar; see Jer 49:34, Jer 49:35. Here was Daniel's ordinary residence; and though here at this time, he, in vision, saw himself on the banks of the river Ulai. This is the same as the river Euleus, which divided Shushan or Susiana from Elymais.