Mnemosyne's domain became, in classical rhetorical training, a formal technique with a name, a legendary inventor, and a long afterlife well beyond ancient religion. Cicero's De Oratore and the anonymous Rhetorica ad Herennium, both Roman handbooks of rhetoric from the first century BCE, describe what later ages came to call the method of loci or the memory palace, a technique in which an orator memorizes a long speech by mentally placing its parts as vivid images at fixed points along an imagined, familiar physical space, a house or a journey, so walking through the space in the mind's eye retrieves the images, and with them the material, in the correct order. Ancient tradition credited the poet Simonides of Ceos with discovering the technique after a banquet hall collapsed and he alone could identify the crushed guests by recalling exactly where each had been sitting, a legendary origin story these Roman sources themselves already treat as received tradition rather than eyewitness fact.
The technique, explicitly framed by its ancient teachers as a discipline in the service of memory and therefore, if only informally, in Mnemosyne's own domain, did not end with antiquity: the Renaissance saw a significant revival of elaborate memory systems, most famously associated with the philosopher Giordano Bruno, and the historian Frances Yates's 1966 study The Art of Memory brought the whole tradition to wide modern scholarly attention. A technique competitive memorizers still use today under the same name, the memory palace, descends in an unbroken line of description, if not necessarily of continuous practice, from the same rhetorical handbooks that first systematized what the goddess of memory's name had always simply implied.