On the news of the Gordians' defeat and death in 238 the Senate met in closed session in the Temple of Jupiter Capitolinus and voted for Pupienus and Balbinus to be installed as co-emperors.
Leaving his senior colleague Balbinus in charge of the civil administration at Rome, sometime during late April Pupienus marched to Ravenna, where he oversaw the campaign against Maximinus, who too strived for the throne.
Balbinus, in the meantime, had failed to keep public order in the capital. Pupienus, becoming aware of the threat, begged Balbinus to call for his bodyguards. Balbinus, believing that this news was part of a plot by Pupienus to have him assassinated, refused, and the two began to argue just as the Praetorians burst into the room. Both emperors were seized and dragged back to the Praetorian barracks where they were tortured and brutally hacked to death. (Source: Wikipedia)