Pliny speaks of his early attempts at poetry:
Ep. vii. 4, 2-3, ‘Numquam a poetice (altius enim repetam) alienus fui; quin etiam quattuordecim natus annos Graecam tragoediam scripsi. Qualem? inquis: nescio: tragoedia vocabatur.’
In Books i.-iii. he appears only as a lover of poetry and a patron of poets (cf. i. 16; iii. 15). From Book iv. (published A.D. 105) onwards he appears as a poet. In Ep. vii. 4, 6 are thirteen poor hexameter lines on Cicero; ibid. §§ 7-8, ‘Transii ad elegos: hos quoque non minus celeriter explicui: addidi iambos, facilitate corruptus ... Postremo placuit exemplo multorum unum separatim hendecasyllaborum volumen absolvere, nec paenitet. Legitur, describitur, cantatur etiam.’ Pliny defends himself for writing light verses in Ep. v. 3, etc. In the later books he refers to another proposed collection of verses.
Ep. viii. 21, 3, ‘Liber fuit et opusculis varius et metris.’
Pliny says he did not observe chronological order in publishing his letters.
Ep. i. 1, 1, ‘Collegi non servato temporis ordine (neque enim historiam componebam), sed ut quaeque in manus venerat.’
This, however, is not convincing, as it falls in with Pliny’s wish to give an appearance of negligence to the work, and besides it may apply only to Book i. Successive publication of the different Books is shown by many references; so Ep. ix. 19, ‘Significas legisse te in quadam epistula,’ where Ep. vi. 10 is referred to. So also contemporaneous events are always described in the same Book or in two Books close together; and when a subject is continued in another letter, the order of the two letters fits in with chronology. So iii. 4 and iv. 1 deal with the building of a temple at Tifernum; iii. 20 and iv. 25 with ballot at elections.
The following are the probable dates of publication: Book i. in A.D. 97; Book ii. in A.D. 100; Book iii. in A.D. 101 or 102; Book iv. in A.D. 105; Book v. in A.D. 106; Book vi. possibly in A.D. 106; Book vii. in A.D. 107; Book viii. not before A.D. 109; Book ix. probably about the same time.
The correspondence with Trajan is independent of the nine Books of letters. The epistles are roughly in chronological order. Epp. 1-14 range from 98 to 106 A.D. Epp. 15 to the end were probably all written in Bithynia during Pliny’s governorship there. Trajan’s reply is subjoined to most of the letters. The correspondence extant stretches from September A.D. 111 over January A.D. 113.
Pliny had intimate relations with other writers, the principal being Tacitus; Martial (cf. Ep. iii. 21); Silius Italicus (cf. Ep. iii. 7). See [pp. 340], [298], [289]. For his literary reputation see Ep. ix. 23, 2, quoted [p. 338] and cf. Ep. i. 2, 6, ‘Libelli quos emisimus dicuntur in manibus esse, quamvis iam gratiam novitatis exuerint; nisi tamen auribus nostris bibliopolae blandiuntur.’