"In the Fifteenth Year" Reconsidered: A Study of Luke 3:1

This study proposes that Luke’s reference to the fifteenth year of the reign
of Tiberius coincides with the year AD 29. Evidence for this comes from
two sources: Augustus’s memoirs and Velleius Paterculus. Those who
have suggested that Augustus and Tiberius had equal positions in Rome
prior to Augustus’s death have examined only the legal powers (potestas)
granted to Tiberius and not the status of Augustus and Tiberius.