Plutarch Galba 24

[1] Among these were Veturius and Barbius the one an optio, the other a tesserarius (these are the Roman names for scout and messenger). In company with these Onomastus, a freedman of Otho’s, went round corrupting the soldiers, some with money, and others with fair promises. The soldiers were already disaffected and wanted only a pretext for treachery. For four days would not have sufficed to change the allegiance of a loyal army, and only so many days intervened between the act of adoption and the murder, since on the sixth day after the adoption (the Romans call it the eighteenth before the Calends of February ¹ ), Galba and Piso were slain.

[2]
  On that day, shortly after dawn, Galba was sacrificing in the Palatium in the presence of his friends; and as soon as Umbricius, the officiating priest, had taken the entrails of the victim in his hands and inspected them, he declared not ambiguously, but in so many words, that there were signs of a great commotion, and that peril mixed with treachery hung over the emperor’s head. Thus the god all but delivered Otho over to arrest.

[3] For Otho was standing behind Galba, and noted what was said and pointed out by Umbricius. But as he stood there in confusion and with a countenance changing to all sorts of colours through fear, Onomastus his freedman came up and told him that the builders were come and were waiting for him at his house. Now, this was a token that the time was at hand when Otho was to meet the soldiers.

[4] With the remark, then, that he had bought an old house and wished to show its defects to the vendors, he went away, and passing through what was called the house of Tiberius, went down into the forum, to where a gilded column stood, at which all the roads that intersect Italy terminate.