The Art of Memory, was said to have been invented by a poet named Simonides (according to Cicero). In a bit of ancient forensics, Simonides had been able to identify the remains of guests at a banquet by their seating places around a table, after a roof had fallen in upon them and obliterated them beyond recognition. In the Classical use of the art, abstract images of a somewhat bizarre (and therefore memorable) nature were conceived that would be linked to parts of a speech and then to a well-known architectural feature of the hall in which the speech was to take place. By scanning the variety of statuary, friezes, articulated columns, or whatever, within the hall, the rhetorician skilled in the art could remember all the aspects of his speech. The hall would provide the order and a frame of reference which could be used over and over again for a complex constellation of constantly changing ideas.
The Classical art of memory evolved in the Middle Ages into an Aristotelian form, in which the construction of a memory image could heighten human perception and therefore aid in the acceptance of a moral lesson which was being communicated. The Middle Ages had somewhat limited possibilities to support a refinement of ideas and observations which sustained the culture. However, with the discovery of the New World and the rediscovery of the Classical World, a sense of wonder was brought back into European thought. Exposure to new cultures and possibilities that existed outside the realm of understanding for Europeans, opened them up to the idea of exploring (as well as subjugating) the world outside of their known universe.
The near simultaneous invention of movable type, and mass printing, produced another technological refinement in the collective knowledge of the then 'known world.' Likewise, the skills of the rhetorician reached their developmental zenith which would then subside as printed knowledge became more available. Curiously, the use of memory systems did not become immediately obsolete with the invention of printing, but instead became elaborated into yet another form as a complex, Neoplatonic magic which would have a far reaching, though somewhat obscured, influence.
Within the hermetic 'soup' of the Italian Renaissance of the sixteenth century, the mnemonic images used in memory systems were believed to be the gateway to a transcendental and ideal reality. The mnemonist rhetorician assumed a role similar to the oral tradition poets, by assuming a position of being the chief interpreter of the nature of reality and the keeper of divine wisdom. By constructing their art accurately, the natural order of reality could be 'recollected,' and the magus/rhetorician would then 'know' the eternal mind of God. Among the more important practitioners of this Neoplatonic form of the art of memory are Giulio Camillo and Giordano Bruno.
Frances A. Yates's works on the subject of the Art of Memory are a starting point for any contemporary study of it, even one as facile as this. They include:
Giordano Bruno and the Hermetic Tradition (Chicago: The University of Chicago Press, 1964 & New York: Vintage Books Paperback, 1969).
The Art of Memory (Chicago: The University of Chicago Press, 1966).
Theatre of the World (Chicago: The University of Chicago Press, 1969).