 Since the Song dynasty, critics have called Du Fu the "poet historian".The most directly historical of his poems are those commenting on military tactics or the successes and failures of the government, or the poems of advice which he wrote to the emperor.One of the Du Fu's earliest surviving works, "The Song of the Wagons" (c. 750), gives voice to the sufferings of a conscript soldier in the imperial army, even before the beginning of the rebellion; this poem brings out the tension between the need of acceptance and fulfillment of one's duties, and a clear-sighted consciousness of the suffering which this can involve.