Pliny the Younger to Maecilius Nepos

Epist. 2.3.3-4 (LCL; trans. B. Radice)

[Isaeus] has an amazing memory, so that he can repeat his extempore speeches word for word without a single mistake, a technique he has developed by application and constant practice; for night and day everything he says and hears and does is directed to this end alone.