According to Suetonius, the second book of "Epistles" was prompted by Augustus, who desired a verse epistle to be addressed to himself. Augustus was in fact a prolific letter-writer and he once asked Horace to be his personal secretary. Horace refused the secretarial role but complied with the emperor's request for a verse letter. The letter to Augustus may have been slow in coming, being published possibly as late as 11 BC. It celebrated, among other things, the 15 BC military victories of his stepsons, Drusus and Tiberius, yet it and the following letter were largely devoted to literary theory and criticism. The literary theme was explored still further in "Ars Poetica", published separately but written in the form of an epistle and sometimes referred to as "Epistles" 2.3 (possibly the last poem he ever wrote). He was also commissioned to write odes commemorating the victories of Drusus and Tiberius and one to be sung in a temple of Apollo for the Secular Games, a long-abandoned festival that Augustus revived in accordance with his policy of recreating ancient customs ("Carmen Saeculare").