Among the correspondence between Pliny and Trajan in Book 10 of Pliny's letters is an exchange about the status (condicio) and rearing costs (alimenta) of threptoi – an issue that, Pliny says, pertained to his entire province of Bithynia and Pontus and required an imperial ruling (Pliny Ep. X.65). Trajan responds that the question of those who were born free but abandoned at birth (liberi nati expositi) and then picked up and reared as slaves had often been the subject of rulings, but there was no empire-wide policy on them. He rules that recovery of freedom by those who could prove their free origin should not be contingent on payment of rearing costs (Ep. X.66). Pliny's letter (as we have it) does not actually define the Greek word he uses, threptoi (literally, "nurtured ones"). Trajan's response (as we have it) does not use the word threptoi, and Pliny's request does not explicitly say that the provincials whose status was of concern were expositi ("placed out ones"). This discrepancy is probably due to later editing, either by Pliny himself (Woolf 2015) or someone else after Pliny's presumed death (cf. Coleman 2012). It is clear, however, that Trajan and his concilium equated the threptoi of Pliny's province with expositi, i.e. those who had been abandoned at birth by their parents. Pliny and Trajan both note that there were previous imperial rulings on threptoi responding to other places in the Greek East, primarily the province of Achaea and the Lacedaimonians (who enjoyed the status of a free city within Achaea). They agree that such rulings were not pertinent to threptoi in Bithynia and Pontus, presumably because the circumstances that prompted claims by threptoi or their rearers were different in mainland Greece than in northern Asia Minor.
I argue that Trajan's equation of threptoi with expositi is inaccurate, and says more about the Roman legal tendency to categorize and define relationships than about who these threptoi actually were. There is considerable epigraphic evidence in the inscriptions of Asia Minor, including Pliny's province, for threptoi. Some are of slave birth, but others are clearly freeborn, and in some cases even of higher status than their rearers. The term threptoi, which "denotes any person, slave or free(born), nurtured by someone other than their natural parents" (Ricl 2009: 94), had far more semantic flexibility than expositi (or even the closest Latin equivalent, alumni). It is this very fluidity of meaning that probably caused problems for Pliny: one size did not fit all, either in Bithynia or Achaea. Threptoi are yet another example of the fictive kin relationships that Roman imperial subjects constructed for themselves, relationships that did not fit within the status hierarchy of Roman law. A careful examination of the epigraphic evidence for threptoi in the Greek east can shed light on the "translation" of provincial mores into Roman policies.
Childhood and Fictive Kinship in the Roman Empire