Was Philippians Paul's last letter

The Epistle to the Romans is generally considered to be Paul's last authentic letter. There are doubts about the authenticity of the Epistle to the Philippians, but whether by Paul or a later disciple in his name, it should be much later than Romans.

Philippians 1:1 refers to the roles of bishops and deacons, roles that do not seem to have become established until the second century when the Church was grown sufficiently to require a hierarchy. At the very least, this would have been a later interpolation inserted into the epistle.