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Senior officer

At the end of AD 69, after a year of civil war consequent on the death of Nero, Vespasian, a successful general, became emperor. Like Pliny, he had come from the equestrian class, rising through the ranks of the army and public offices and defeating the other contenders for the highest office. His main tasks were to re-establish peace under imperial control and to place the economy on a sound footing. He needed in his administration all the loyalty and assistance he could find. Pliny, apparently trusted without question, perhaps (reading between the lines) recommended by Vespasian's son Titus, was put to work immediately and was kept in a continuous succession of the most distinguished procuratorships, according to Suetonius. A procurator was generally a governor of an imperial province. The empire was perpetually short of, and was always seeking, officeholders for its numerous offices.

Throughout the latter stages of Pliny's life, he maintained good relations with Emperor Vespasian. As is written in the first line of Pliny the Younger's Avunculus Meus:

Ante lucem ibat ad Vespasianum imperatorem (nam ille quoque noctibus utebatur), deinde ad officium sibi delegatum.

Before dawn he was going to Emperor Vespasian (for he also made use of the night), then he did the other duties assigned to him.

In this passage, Pliny the Younger conveys to Tacitus that his uncle was ever the academic, always working. The word ibat (imperfect, "he used to go") gives a sense of repeated or customary action. In the subsequent text, he mentions again how most of his uncle's day was spent working, reading, and writing. He notes that Pliny "was indeed a very ready sleeper, sometimes dropping off in the middle of his studies and then waking up again."

A definitive study of the procuratorships of Pliny was compiled by the classical scholar Friedrich Münzer, which was reasserted by Ronald Syme and became a standard reference point. Münzer hypothesized four procuratorships, of which two are certainly attested and two are probable but not certain. However, two does not satisfy Suetonius' description of a continuous succession. Consequently, Plinian scholars present two to four procuratorships, the four comprising (i) Gallia Narbonensis in 70, (ii) Africa in 70–72, (iii) Hispania Tarraconensis in 72–74, and (iv) Gallia Belgica in 74–76.

According to Syme, Pliny may have been "successor to Valerius Paulinus", procurator of Gallia Narbonensis (southeastern France), early in AD 70. He seems to have a "familiarity with the provincia ", which, however, might otherwise be explained. For example, he says

In the cultivation of the soil, the manners and civilization of the inhabitants, and the extent of its wealth, it is surpassed by none of the provinces, and, in short, might be more truthfully described as a part of Italy than as a province.

denoting a general popular familiarity with the region.

Pliny certainly spent some time in the province of Africa, most likely as a procurator. Among other events or features that he saw are the provoking of rubetae, poisonous toads (Bufonidae), by the Psylli; the buildings made with molded earthen walls, "superior in solidity to any cement;" and the unusual, fertile seaside oasis of Gabès (then Tacape), Tunisia, currently a World Heritage Site. Syme assigns the African procuratorship to AD 70–72.

The procuratorship of Hispania Tarraconensis was next. A statement by Pliny the Younger that his uncle was offered 400,000 sesterces for his manuscripts by Larcius Licinius while he (Pliny the Elder) was procurator of Hispania makes it the most certain of the three. Pliny lists the peoples of "Hither Hispania", including population statistics and civic rights (modern Asturias and Gallaecia). He stops short of mentioning them all for fear of "wearying the reader". As this is the only geographic region for which he gives this information, Syme hypothesizes that Pliny contributed to the census of Hither Hispania conducted in 73/74 by Vibius Crispus, legate from the Emperor, thus dating Pliny's procuratorship there.

During his stay in Hispania, he became familiar with the agriculture and especially the gold mines of the north and west of the country. His descriptions of the various methods of mining appear to be eyewitness judging by the discussion of gold mining methods in his Natural History. He might have visited the mine excavated at Las Médulas.

The last position of procurator, an uncertain one, was of Gallia Belgica, based on Pliny's familiarity with it. The capital of the province was Augusta Treverorum (Trier), named for the Treveri surrounding it. Pliny says that in "the year but one before this" a severe winter killed the first crops planted by the Treviri; they sowed again in March and had "a most abundant harvest." The problem is to identify "this", the year in which the passage was written. Using 77 as the date of composition Syme arrives at AD 74–75 as the date of the procuratorship, when Pliny is presumed to have witnessed these events. The argument is based entirely on presumptions; nevertheless, this date is required to achieve Suetonius' continuity of procuratorships, if the one in Gallia Belgica occurred.

Pliny was allowed home (Rome) at some time in AD 75–76. He was presumably at home for the first official release of Natural History in 77. Whether he was in Rome for the dedication of Vespasian's Temple of Peace in the Forum in 75, which was in essence a museum for display of art works plundered by Nero and formerly adorning the Domus Aurea, is uncertain, as is his possible command of the vigiles (night watchmen), a lesser post. No actual post is discernible for this period. On the bare circumstances, he was an official agent of the emperor in a quasiprivate capacity. Perhaps he was between posts. In any case, his appointment as commander of the imperial fleet at Misenum took him there, where he resided with his sister and nephew. Vespasian died of disease on 23 June 79. Pliny outlived him by four months.