In the bathhouse inscription we mentioned above, we saw that Pliny's full title as governor of Bithynia-Pontus was legatus Augusti pro praetore consulari potestate ex senatusconsulto missus. This is not an ordinary title. The first four words are the normal name of the governor of one of the imperial provinces. However, Bithynia was not an imperial province. It was senatorial, and the governor was called proconsul. (Imperial provinces were governed by the emperor, senatorial provinces by the Senate.) Therefore, Pliny was ex senatusconsulto missus, which means that he was sent in accordance with a Senate's decree. Finally, the words consulari potestate mean that the new governor had full consular powers. This was most unusual.
But there are other irregularities. Usually, a governor was in his thirties. Pliny was forty-seven, and had proportionally more experience. He was also well-informed about the province. After all, he had defended two accused governors of Bithynia.
It is also interesting to note the length of his stay. We possess the entire correspondence between Trajan and Pliny. The governor's first letter was written on 17 September 109, and the last datable letter on 28 January 111. After this message, Pliny wrote several other letters, but if he continued to write at the normal frequency, his last letter was written in March or April. This means that he was in office for eighteen months, which is strange, because the proconsul of a senatorial province typically served twelve months and the governor of an imperial province thirty-six.
Did Pliny die in office? Several scholars believe this, but it is not likely. He was not even fifty, and it appears that he was in excellent shape, because he traveled extensively across his province. Moreover, his last letter deals with Calpurnia's departure for Italy, and it would be rather heartless if she had left her dying man alone.
A possible but very speculative explanation for the eighteen months' stay is that Trajan was thinking about a censorship when he sent his special governor to the east. A censor was a former consul who had to control the books of financial institutions and large-scale building projects. The office no longer existed (Domitian had added the tasks to those of the emperor), but it is remarkable that Pliny's assignment also involved financial controlling of public works. Did Trajan think of this old magistracy when he sent Pliny to Bithynia? We will never know, but it is possible.
However this may be, it is a fact that Pliny governed his province for eighteen months and had extraordinary powers. Moreover, never before had the emperor sent a governor to a senatorial province. In our words, Pliny served as an interim-manager.