Comment
The narrative about this double coup does not sound very convincing, but we can corroborate Herodotus' story, because the same story is told in Darius' Behistun inscription. The main difference is that in Darius' story there is only one Magian, named Gaumâta, who seizes power and has himself called Bardiya (sections 10-15). Herodotus' duplication must be due to a misunderstanding of this man's title: Patizeithes is the Greek form of patikhayathya or 'governor'. Probably, he heard about the patikhayathya who called himself Bardiya, and erroneously thought that there were two men involved.
From the inscription, we know that Bardiya/Smerdis seized power on March 11, 522 BCE, that Cambyses died in July in Syria, hurrying home to suppress the rebellion, that there was a conspiracy of seven noblemen, who killed the false king on September 29. A point of some interest is the resemblance of the names of the conspirators, who are mentioned in section 68 of the Behistun inscription.
FOR THE BEHISTUN INSCRIPTION GO HERE"
http://atlantisonline.smfforfree2.com/index.php/topic,2799.0.html Herodotus' names Persian names
Otanes, son of Pharnaspes Utâna, son of Thukra
Gobryas, father of Mardonius Gaubaruva, son of Marduniya
Intaphrenes Vindafarna, son of Vayâspâra
Hydarnes Vidarna, son of Bagâbigna
Megabyzus Bagabuxa, son of Dâtuvahya
Darius Dârayavau
Aspathines Ardumani, son of Vakauka
Darius. Relief from the
northern stairs of the Apadana
at Persepolis (Archaeological
museum, Tehran)
This means that Herodotus has only one name wrong: instead of Ardumani he mentions Aspathines. We may assume that the mistake was made by Herodotus' Persian spokesman: Aspaçânâ was a very important courtier.
The list of satrapies closely resembles comparable documents from ancient Persia, the Empire lists (e.g., section 6 of the Behistun inscription, the inscription on Darius' grave and the Daiva inscription by Xerxes - go here for a comparison of these texts). There are some minor inconsistencies, however, which cannot be explained.
The story about Zopyrus ending the revolt of Babylon is unlikely to be true in its present form, although comparison with section 32 of the Behistun inscription makes it clear that this type of mutilation was not uncommon. Probably, the story is inspired by Homer's description of Odysseus, who was able to spy in Troy after mutilating himself (Odyssey 4.240-246). No Zopyrus is known from Babylonian cuneiform texts.
The Behistun inscription also informs us about two rebellions in Babylon, one under Nidintu-Bęl, who assumed the throne name Nebuchadnezzar, and one under the Armenian Arakha, who assumed the same name. The first of these two rebels revolted on 3 October 522 and was captured by Darius on 18 December; the second rebel ruled from 25 August 521 until 27 November and was defeated by Hydarnes, one of the seven conspirators. In the same period, there were two rebellions in Elam, one in Sagartia, one in Margiana, one in Persia, and one in Media (mentioned briefly by Herodotus, who does not mention that Darius' father Hystaspes was one of the Persian commanders in this theater of operations).
Literature
Andrew R. Burn, Persia and the Greeks. The Defence of the West, c.546-478 B.C. (1962 London) pages 81-104
Albrecht Dihle, 'Arabien und Indien' in: Hérodote et les peuples non Grecs. Neuf exposés suivis de discussions (Entretiens sur l' Antiquité classique, tome XXV) (1990 Genčve), pages 41-67
http://www.livius.org/he-hg/herodotus/logos3_08.html