When one Tiberius Petasius proclaimed himself emperor in Tuscia .
Eutychius found himself critically short of manpower , Pope Gregory ordered the Roman army to help him put down the rebellion , and Tiberius Petasius was killed .
When one Tiberius Petasius proclaimed himself emperor in Tuscia and Eutychius found himself critically short of manpower , Pope Gregory ordered the Roman army to help him put down the rebellion , and Petasius was killed .