consul in Fasti), was the commander
of the fifteenth legion in Pannonia, with which he was sent to join Corbulo in his expedition
against the Parthians in 64. On the death of Nero in 68, Celsus joined Galba's party, at which
time he is spoken of as consul designatus, but whether he had been nominated to the consulship
by Nero or by Galba is uncertain. He was one of the ablest and most faithful of Galba's
supporters; and when the troops rebelled against the new emperor, Celsus was sent to endeavour
to propitiate the detachment of the Illyrian army which had encamped in the Vipsanian
porticus. It was probably thought that Celsus would have more influence with this army than
any one else, on account of his former connexion with it: but he was unable to quell the
insurrection. The death of Galba soon followed, and Otho obtained the sovereignty. The life of
Celsus was now in great danger; the partizans of Otho loudly demanded his execution; but Otho,
who appreciated his fidelity to his late master, not only spared his life, but admitted him to
the circle of his most intimate friends. Celsus served Otho with the same fidelity as he had
the late emperor. He was sent, together with Suetonius Paullinus and Annius Gallus, in command
of the army to oppose the generals of Vitellius, who were advancing into Italy. At first he
and his colleagues were completely successful; in the campaign on the Po, in the neighbourhood
of Placentia and Cremona, they defeated all the plans of Caecina, the general of Vitellius
[CAECINA, No. 9]; and it was not till the latter had been joined by
Fabius Valens, and Otho had resolved, against the advice of Celsus as well as Suetonius
Paullinus, to risk a battle, that the aspect of affairs was changed. The battle of Bedriacum,
in which Otho's army was defeated, gave Vitellius the empire; but Celsus, who had remained
faithful to Otho to the last, again did not suffer for his fidelity. Vitellius allowed him to
enter on the consulship on the calends of July (Hist. 1.14, 31, 39, 45, 71, 77, 87, 90, 2.23, 33, 60.)