was consular legate of the army of Upper Germany at the time of Nero's death (A. D. 68).
He was despised by his army, for he was old, a cripple, without firmness, and without influence. When his soldiers renounced allegiance to Galba (Jan. 1. 69 A. D.), he had not the courage to oppose them, though he did not share in their treason.
He was left in command of the left bank of the Rhine by Vitellius, when the latter marched to Italy; but he delayed the march of the forces which Vitellius sent for from the Germanies, partly through fear of the insurrection of the Batavians, which soon after broke out, and partly because in his heart he favoured Vespasian.
He even requested Civilis to assist in retaining the legions, by pretending to raise a rebellion among the Batavians; which Civilis did, not in pretence, but in earnest. [CIVILIS.] Flaccus took no notice of the first movements of the Batavians, but their success soon compelled him to make at least a show of opposition, and he sent against them his legate, Mummius Lupercus, who was defeated.
By the proofs he gave of his unwillingness or inability to put down the insurrection, and by receiving a letter from Vespasian, he exasperated his soldiers, who compelled him to give up the command to VOCULA. Shortly afterwards, in a fresh mutiny during the absence of Vocula, he was accused of treachery by HERENNIUS GALLUS, and, as it seems, was bound by the soldiers, but he was released again by Vocula.
He still however retained sufficient influence to persuade the army to take the oath to Vespasian, when the news arrived of the battle of Cremona.
But the soldiers were still mutinous; and on the arrival of two fresh legions, they demanded a donative out of some money which they knew had been sent by Vespasian. Hordeonius yielded to the demand : the money was spent in feasting and drinking; the soldiers, thus excited, recalled to mind their old quarrel with Hordeonius, and, in the middle of the night, they dragged him from his bed and killed him. (Tac. Hist. 1.9
. 56, 2.57, 97, 4.13, 18, 19, 24, 25, 27, 31, 36, 55, 5.26; Plut. Galba,
10, 18, 22.)