This chapter looks at two interconnected texts which were published within two or three decades of each other. I begin with Aelianus Tacticus' Tactical Theory, a treatise which harks back to a bygone age in Greek military history. 1 It draws on works which themselves looked back to Polybius and earlier, 2 and thus sets out prescriptions for the organisation and formation of troops which derive from the Classical and Hellenistic periods. Consciously archaising, it is also heavily derivative: much of it appears to be a reproduction of a lost treatise by the Stoic philosopher Posidonius, the same text which Arrian seems to have drawn on in his Tactics two or three decades later. 3 Arrian must have been aware of Aelian's treatise (the texts were presumably written and read within similar circles), which means that he compiled his own rewrite of Posidonius' original in conscious relation to Aelian's version, and perhaps in the expectation that readers would compare the two. There is no direct interaction, but the differences between the texts-and their respective interactions with other texts and authorityfigures-offer an opportunity to explore different models of literary and cross-cultural interaction, occurring across language barriers, between different levels of social and political authority, and between different kinds of writing. Aelian's interactions with Frontinus Aelian begins the preface to his Tactical Theory in time-honoured fashion by explaining his reasons for writing. He anchors his efforts in a long-established Greek military writing tradition * I am grateful to Rebecca Langlands, James Uden and CUP's anonymous readers for their feedback on various drafts of this chapter. 1 On its date (sometime between 106 and 113), see Dain 1946: 18-19; Devine 1989: 31. Hereafter, I will refer to Aelianus Tacticus simply as Aelian, not to be confused with Steven Smith's Aelian later in this volume. 2 Devine 1995. 3 The exact relationship between these texts remains a matter of debate (for run-down of views, see Devine 1989: 32-3; Stadter 1978), with Asclepiodotus' Tactics also part of the picture. Arrian notes at Tact. 44 that he was writing in the twentieth year of Hadrian's reign, thus around 136-137.