Eratosthenes of Cyrene (276–194 b.c.e.), the third head of the Alexandrian Library, sent a letter to King Ptolemy outlining his solution for the geometric problem, the doubling of the cube. Although traditionally the preserve of historians of mathematics, the text quotes from tragedy, recounts mathematical research at Plato's Academy, and concludes with an epigram. Here, I address each generic gesture and its particular audience and aim. This article reads the letter not only as a dynamic unified whole which innovatively integrates mathematics and literature, but as a text which lays out the mechanics of the Ptolemaic empire for its readership.