For the history of the Roman administration in the early Imperial period we would seem to be well placed. There is an abundance of data on officials at all levels, their functions, careers, families, status and power – and from sources of every kind, literary, epigraphic, juridical, papyrological and archaeological. We know of hundreds, even thousands of such officials. The time would therefore seem ripe for not only a comprehensive descriptive account of the Imperial administration but also for a structural analysis of the system itself, the relationship to one another of the main institutional elements that constituted it: the emperor, the senatorial and equestrian hierarchy, the Imperial freedman and slave officials, and the interaction of all these with administration at municipal level. But a prime requirement for such an account and analysis is the assurance that we can organize the data and place the officials in the right chronological order. A reliable chronology is essential if we are to trace institutional change in the medium and short term. In this regard the Imperial freedman and slave officials are of major importance. In training and experience they make up the professional ‘civil service’ of the early empire – as contrasted with the relatively ‘amateur’ administrative role played by senatorial legati and equestrian procuratores, whose more spasmodic careers were more susceptible to influences of patronage. But it is precisely in the careers of the Imperial freedmen and slaves that chronological problems are most acute and caution most necessary, partly because of the numbers involved and partly in the interpretation of nomenclature.