The kings of Persia mentioned of in the Bible can be a little confusing to differentiate, especially when they share the same name. Here we shall take a moment to add clarity on this subject.
Cyaxares (also known as Ahasuerus I) and Astyages were the last two kings of Medo-Persia whilst Babylon was the superpower. After Babylon fell and Persia became the new world power, Cyrus II (whose grandfather was Cyrus I]) became its king, and is mentioned of in Ezra 1: 1: Now in the first year of Cyrus king of Persia, that the word of the LORD by the mouth of Jeremiah might be fulfilled, the LORD stirred up the spirit of Cyrus king of Persia, that he made a proclamation throughout all his kingdom, and put it also in writing, saying,
In Ezra 4: 6, we read of Ahasuerus: And in the reign of Ahasuerus, in the beginning of his reign, wrote they unto him an accusation against the inhabitants of Judah and Jerusalem. His actual name was Cambyses II (whose grandfather was Cambyses I). He reigned after his father Cyrus II, and was also known as Ahasuerus II (for Cyaxares was Ahasuerus I).
In Ezra 4: 7, we read of Artaxerxes: And in the days of Artaxerxes wrote Bishlam, Mithredath, Tabeel, and the rest of their companions, unto Artaxerxes king of Persia; and the writing of the letter was written in the Syrian tongue, and interpreted in the Syrian tongue. His actual name was Bardiya or Smerdis. He was the younger brother of Cambyses II and reigned after him.
In Ezra 4: 24 we read of Darius: Then ceased the work of the house of God which is at Jerusalem. So it ceased unto the second year of the reign of Darius king of Persia. He was Darius I (also known as Darius Hystaspes, the son of Hystaspes). He reigned after Smerdis.
Xerxes I (also known as Ahasuerus III) was the son of Darius I, and is the King mentioned of in the Book of Esther who took her to wife and made her queen. The story of Esther actually unfolds between the sixth and seventh chapters of the Book of Ezra.
In Ezra 7: 1 we read of Artaxerxes I: Now after these things, in the reign of Artaxerxes king of Persia, Ezra the son of Seraiah, the son of Azariah, the son of Hilkiah, He was the son of Xerxes I and is the last of the Persian kings mentioned of in the Book of Ezra.
The Bible records the following in Daniel 5: 30 – 31: In that night was Belshazzar the king of the Chaldeans slain. And Darius the Median took the kingdom, being about threescore and two years old. When Babylon fell, it is said that Darius the Median took the kingdom. Now the question will arise as to how this correlates with what we said earlier that Cyrus II was King when Persia became the new world power. This is quite simple to answer, for Darius the Median was made the governor of Babylon under Cyrus II, in much the same way as Belshazzar was said to be the King of Babylon, but he was actually the sub-ordinate ruler under Nabonidus (Daniel 5: 29) who was the supreme ruler of Babylon.
Let us summarize our examination of Persia’s rulers. The Persian Empire was truly begun under Cyrus II (he was also known as Cyrus the Great) when he conquered Babylon. It was Cyrus II who issued the decree for the Jews to return to their homeland to rebuild their temple. Later, under Darius I (Hystaspes), the Jews’ second temple was completed (by Zerubbabel). Under Xerxes I (Ahasuerus III) the events recorded in the Book of Esther took place; and under Artaxerxes I, the Jewish State was reformed (by Ezra) and the walls of Jerusalem were rebuilt (by Nehemiah).