How did Otho become emperor? Praetorian acclamation and Senate ratification on the same day
On 15 January 69 CE, Otho was proclaimed emperor by the Praetorian Guard and ratified by the Senate before the day ended. Hailed by 23 praetorian scouts at the Golden Milestone, he was rushed to the camp as Galba was cut down in the Forum.
At the height of Rome’s crisis in January 69, Otho slipped away from Galba’s sacrifice on the Palatine, crossed through the Tiberian house to the Velabrum, and at the Milliarium Aureum was saluted imperator by twenty-three speculatores. Hoisted into a sedan-chair and hurried to the Praetorian camp, he rode the Guard’s revolt—stoked by Galba’s stinginess and a promised donative—to the throne. That same day, as Galba and Piso were murdered in the Forum, the city praetor convened the Senate, which voted Otho tribunician power and the name Augustus. Otho appeared, claimed he had been compelled, and retired to the palace: acclamation first, constitutional ratification immediately after.
Key Factors
Praetorian acclamation at the Golden Milestone
While Galba performed sacrifices, Otho slipped out via the Tiberian house to the Milliarium Aureum, where twenty-three speculatores hailed him imperator. The guards set him in a chair and rushed him to the Praetorian camp, giving him the muscle to claim power.
Same‑day Senate ratification
As news of Galba’s murder spread, the city praetor convened the Senate. Before nightfall, senators granted Otho tribunician power and the title Augustus, clothing the Guard’s coup in constitutional legitimacy.
Donatives and Guard discontent
Galba’s refusal to pay a promised donative—and his proud boast that he ‘chose, not bought, his soldiers’—left the Guard resentful. Otho capitalized on this anger and outbid Galba’s austere image, aligning money, momentum, and manpower.
Timing amid a militarized succession
With Vitellius already acclaimed by the Rhine legions on 2 January, the army’s role in making emperors was unmistakable. Otho’s plot—triggered by Galba’s adoption of Piso—moved swiftly on 15 January, pairing street power with senatorial assent.
Historical Evidence
"Twenty‑three speculatores hailed Otho at the Milliarium Aureum and hurried him to the Praetorian camp (15 January 69)."
"The Senate, called by the city praetor, voted him tribunician power and the title Augustus the same day."
"Otho addressed the Senate “towards the close of the day,” claiming he had been “carried off in the streets and forced to undertake the rule.”"
"Galba was slain near the Lacus Curtius in the Forum; Piso was dragged from the Temple of Vesta."
Part of Assassination of Galba and Otho's Accession
This episode is the hinge of the Assassination of Galba and Otho’s Accession (69): the Praetorian Guard made the emperor and the Senate made it official. It also sets the Year of the Four Emperors’ pattern—competing military acclamations ratified in Rome—leading directly to Otho’s clash with Vitellius.