Both The Encyclopedia Americana and the Great Soviet Encyclopedia agree that Artaxerxes’ reign ended in 424 B.C.E. When did it begin? In 474 B.C.E. In support of this, one archaeological inscription is dated in Artaxerxes’ 50th year; another indicates that he was succeeded in his 51st year. Counting back 50 complete years from 424 B.C.E., we come to the date 474 B.C.E. as the start of his reign. Therefore, Artaxerxes’ 20th year, when the command was given, would be 19 complete years into his reign, that is, 455 B.C.E. For further details, see Insight on the Scriptures, Volume 2, page 616, published by the Watchtower Bible and Tract Society of New York, Inc.