In AD 46, at about age 23, Pliny entered the army as a junior officer, as was the custom for young men of equestrian rank. Ronald Syme, Plinian scholar, reconstructs three periods at three ranks. Pliny's interest in Roman literature attracted the attention and friendship of other men of letters in the higher ranks, with whom he formed lasting friendships. Later, these friendships assisted his entry into the upper echelons of the state; however, he was trusted for his knowledge and ability, as well. According to Syme, he began as a "praefectus cohortis", a "commander of a cohort" (an infantry cohort, as junior officers began in the infantry), under Gnaeus Domitius Corbulo, himself a writer (whose works did not survive) in Germania Inferior. In AD 47, he took part in the Roman conquest of the Chauci and the construction of the canal between the rivers Maas and Rhine. His description of the Roman ships anchored in the stream overnight having to ward off floating trees has the stamp of an eyewitness account.