Quintilian, Training of the Orator 11.2.17
Quintilian is discussing mnemonic systems. Simonides’ system (allegedly developed after he identified crushed dinner-party guests from the seats where he remembered they were sitting) involves the recall of places and how associating them with ideas can make memorisation easier. Quintilian agrees that one easily associates certain places with certain memories:
ex hoc Simonidis facto notatum videtur iuvari memoriam signatis animo sedibus, idque credet suo quisque experimento. nam cum in loca aliqua post tempus reversi sumus, non ipsa agnoscimus tantum sed etiam quae in iis fecerimus reminiscimur, personaeque subeunt, nonnumquam tacitae quoque cogitationes in mentem revertuntur. nata est igitur, ut in plerisque, ars ab experimento.
From this achievement of Simonides it seems to have been noticed that memory is helped by locations impressed on the mind – a thing which everyone can try out for themselves, because when we have returned to places after some time we not only recognise the places themselves but can also remember the things we did there; people too come into our heads – and often even unspoken thoughts return to our minds. So, as in most things, a skill is begotten by experiment.