Calvinus had been obliged to despatch to Egypt two out of the three legions left behind with him and formed out of the Pharsalian prisoners of war; he filled up the gap by one legion hastily gathered from the Romans domiciled in Pontus and two legions of Deiotarus exercised after the Roman manner, and advanced into Lesser Armenia.

But the Bosporan army, tried in numerous conflicts with the dwellers on the Black Sea, showed itself more efficient than his own.
Calvinus Defeated at Nicopolis Victory of Caesar at Ziela In an engagement at Nicopolis the Pontic levy of Calvinus was cut to pieces and the Galatian legions ran off; only the one old legion of the Romans fought its way through with moderate loss.
Instead of conquering Lesser Armenia, Calvinus could not even prevent Pharnaces from repossessing himself of his Pontic "hereditary states," and pouring forth the whole vials of his horrible sultanic caprices on their inhabitants, especially the unhappy Amisenes (winter of 706-707).

When Caesar in person arrived in Asia Minor and intimated to him that the service which Pharnaces had rendered to him personally by having granted no help to Pompeius could not be taken into account against the injury inflicted on the empire, and that before any negotiation he must evacuate the province of Pontus and send back the property which he had pillaged, he declared himself doubtless ready to submit; nevertheless, well knowing how good reason Caesar had for hastening to the west, he made no serious preparations for the evacuation.

He did not know that Caesar finished whatever he took in hand.

Without negotiating further, Caesar took with him the one legion which he brought from Alexandria and the troops of Calvinus and Deiotarus, and advanced against the camp of Pharnaces at Ziela.