Nehemiah went to Judah in 445 BC, the 20th year of Persian king Artaxerxes (Neh 1:1, 2:1). Nehemiah had been a cupbearer to the Persian king (Neh 1:1). Nehemiah rebuilt the walls of Jerusalem (part of a confrontation with the Samaritans), battled social injustice in Jerusalem (Neh 5) and built upon Ezra’s reforms.
The books of Ezra and Nehemiah consist of various unrelated documents strung together by an editor. The editor incorrectly dated the missions of Ezra and Nehemiah, though. Rather than the former preceding the latter, Nehemiah likely left Susa for Jerusalem in 445 BC; and Ezra likely arrived in Jerusalem much later, around 398 BC under Persian king Artaxerxes II.