Of all of the characters in the first section of the Anabasis, Clearchus is among the most important, and perhaps the most intriguing.
In Clearchus’s obituary, Xenophon describes a ruthless officer who is feared by all, respected by all, and liked by none(II,6). Clearchus was also the only Greek general who knew from the outset what Cyrus intended to do with the army he was raising(III, 1 (10)). Two questions are very much worth contemplating:
For whom was Clearchus working? And: who is responsible for his death?
The simple answer to the first is that Clearchus was working for Cyrus, as the narrative recounts. The narrative also allows the following interpretation: that Clearchus was using Cyrus to obtain sufficient treasure and military power to install himself as a King somewhere in the Hellenic world. There is a third possibility however: that Clearchus was in the employ of Artaxerxes, charged with tempting Cyrus to attempt a coup, and, if successful, delivering him to Persia and his death. If you imagine that this was his mission, he succeeded in this as well.
At Tarsus and then Thapsacus, the Greeks assembled by Clearchus finally realize that they (I,3 and I,4) are on expedition to overthrow the king of Persia, not to raid his westernmost Satraps. At this juncture, the disaster that has befallen them is evident to most of them, but not laid out in detail for the reader. It’s worthy of some reflection. First, you cannot, as a mercenary, withdraw from employment without badly damaging your subsequent prospects. The rulers of Greece would never have allowed a large number of Greeks to participate in such an expedition, for fear of punitive war from the Persians should it fail. If the expedition failed, the Greek troops were likely to perish en masse in Mesopotamia or Persia proper. Orderly retreat from such a disaster over such an immense distance through hostile territory is highly improbable. In defeat, few or none of the Greeks would return home. If Cyrus had prevailed, he would have required the Greeks to remain in Persia, to help solidify his control of his empire. In this instance, the Greeks are stuck in Persia indefinitely, and Clearchus is the power behind the throne. Worse, the Greek generals are likely to become caught up in Persian palace intrigues, and divided and slaughtered over time. It is certain that Cyrus will honor his promises of rich compensation for his Greek mercenaries; his survival in the short term depends upon them. If and when the Greeks were released from Cyrus’s service, the Spartans would not welcome an army of such power back into Greece. Rather, they would destroy it so that it did not destabilize the balance of power and initiate a downward spiral into another civil war. Clearchus played his fellow Greeks, and put them in a situation where it was very unlikely that they would ever return to Greece.
Fast forward to the end of the day at Cunaxa. Cyrus is dead. Clearchus is still the leader of the Greeks, but is much a dead man as his patron Cyrus. If Clearchus was in fact an agent of Artaxerxes, then Artaxerxes would want him dead ASAP to prevent him from leveraging this knowledge with other Persian nobility. If you are Artaxerxes and you regard Clearchus as the genius behind Cyrus’s campaign and his most trusted confidant, then you want him dead for the role he played in attempting to overthrow you. As the narrative suggests, the slaughter of Clearchus and the other senior leaders would appear to make the subsequent destruction of the remaining leaderless Greek forces much less problematic. There are no upsides for Artaxerxes to allow Clearchus to live. If you are any of the Greeks, you hearken back to Tarsus and Thapsacus, and realize that Clearchus’s treachery is responsible for the disastrous position you are now in. You want him dead, and everyone he identifies as a trustworthy lieutenant too. You have no doubt that he will sell any or all of you out to anyone to preserve his hide or advance his fortunes, as he has already done so once. It makes one wonder: did any of the surviving Greek leaders have anything to do with the death of Clearchus?
When Cyrus dies at Cunaxa, the destruction of Clearchus becomes a certainty.