I was at. I was in. Daniel may have retired there (during the lycanthropy of Nebuchadnezzar) when Nehemiah and Mordecai were in the court of Astyages (Nehemiah 1:1). That Daniel was there employed by Astyages is clear from Daniel 8:27.
Shushan. The chief city of all Persia.
river. Hebrew. 'ubal = canal. Only here, and in verses: Daniel 8:3; Daniel 8:6.