A mandala is a memory palace
Maṇḍalas and memory palaces: that's the theme of something I might have written, had I managed to stay in the academic world. The idea is that the intricate visualisations peformed by a Tantric adept during a ritual work as keys to remembering doctrine, in the same way as Roman orators and renaissance scholars used 'memory palaces' to organise their knowledge. And because all these groups relied on their memories more than we do, they were immeasurably better at putting them to good use.
A lot of Buddhists, modern and ancient, would have a hard time understanding the point of a ritual like this one, where they visualise a kind of hideous monster:
terrible indeed, roaring 'PHAT', adorned with skull ornaments, with sixteen legs, naked, ithyphallic, left legs extended, with a great belly, with hair standing upright, causing great fear, roaring 'pheṃ', with thirty‐four arms and holding a fresh elephant skin [From the Vajrabhairava Tantra]
But when you read the commentary, all this is explained in terms of traditional Buddhist doctrines:
he is ornamented with skull ornaments because he is born from the sphere of dharmas...his sixteen legs are the complete ascertainment of the sixteen emptinesses...he is naked because he understands without obscuration all dharmas....he is ithyphallic because he becomes the great bliss...his left legs are extended because all dharmas are individually penetrated by emptiness...His hair standing up is a sign of his freedom from suffering....The thirty-four arms are the complete ascertainment of the thirty-four aspects of bodhi
Yes, some of the connections are a bit dubious (the usual argument is that the commentators were taking bizarre, transgressive rituals and trying to make them seem orthodox) ‐ but the principle is clearly there: visualise something colourful, and it'll help you remember what`s going on.
In fact, this isn't new. Buddhism was designed from the start to be easy to remember. Why do you have four noble truths, a noble eightfold path, five aggregates, and so on? Because lists are easy to remember, and when you're a wandering monk with only a bowl and a robe for company, you need to keep things in your head.
But go back to that odd Tantric visualisation, because things get even more 
interesting here. It isn't just many-armed gods that were being pictured here, but maṇḍalas with intricate patterns of lines and symbols. One of the underlying themes is the one known in the West by the tag "as above, so below" and in India by "tat tvam asi": i.e. that the maṇḍala represents the world as a whole. And by meditating on aspects of the maṇḍala, you can recall what you have been taught about the universe.
Apart from the Buddhism, this isn't so different from something similar in Europe. Cicero used this 'ars memorativa' to remember his speeches, but the most detailed surviving source is Quintilian, who describes a memory method based on placing symbols of things to be remembered around a home. It's quite similar to the Indian method, except based around a real building not an imagined maṇḍala, and aimed at the law-courts not at religion. It all fits far too comfortably into stereotypes of practical Rome and the mystic East, doesn't it?
This 'art of memory' dribbles on through the centuries, and gets a shot in the arm in the Renaissance, as it's picked by by people like Robert Fludd (who develops a memory palace possibly based on the Globe theatre) and Giordano Bruno (who was famous as a mnemonicist long before the Church burned him as a heretic). These people were still talking about 'memory palaces', but they were moving them away from Quintilian's real buildings and closer to the imagined spaces of Indian rituals.
Now, although I did find one tantilising suggestion of contact between Indian and European mnemonicists, I don't think they're sharing ideas. They've independently come up with similar techniques, because they work.
And that's partly why I'm so fascinated: this is one of the few areas where the modern world lags massively behind the great cultures of history. The mnemonics we retain are laughable shadows. Libraries, computers and cheap paper function as our outboard brains so we don't need onboard brains in the form of maṇḍalas and memory palaces.
In turn, that makes this one of the few areas where humanities scholars can justify their existence. Bringing back these old techniques, and combining for the first time the memory techniques of India, Europe, and anywhere else, is a project that would contribute something useful to the knowledge circulating in our culture. I almost wish I'd stayed in a university, so I could do it.
Mnemonics East and West: I don't seriously think that there was any direct interconnection between Indian and European mnemonic traditions, but I did find this intriguing line in the Ars Memorativa, a memory guide printed in Germany in 1490:
There are some masters who use loci other than doors. Such as chairs, benches, tables, bridges, windows or villages. But they recognise that the door is the easiest to know. Those from India paint in their loci like in a book, like birds, animals, fish. First they have an eagle, then a sparrowhawk, thirdly a hawk, etc. Some from Chaldea use all sorts of strange things. They paint sheep, birds, carts, wheels, horses....
Almost certainly, the author here (who, to be honest, seems to be something of a hack) is just using 'India' to mean 'some wacky far-out place'. But you never know, I could be wrong.
Quintilian: He wrote a full chapter on the art of memory, going through his method in detail. Summarising the crucial bits:
Some place is chosen of the largest possible extent and characterised by the utmost possible variety, such as a space house divided into a number of rooms. Everything of note therein is carefully committed to the memory...
The next step is to distinguish something [to be remembered] by some particular symbol which will serve to jog the memory....
These symbols are then arranged as follows. The first thought is placed, as it were, in the forecourt; the second, let us say, in the living-room; the remainder are placed in due order all round... and entrusted not merely to bedrooms and parlours, but even to the care of statues and the like. This done, as soon as the memory of the facts requires to be revived, all these places are visited in turn and the various deposits are demanded from their custodians, as the sight of each recalls the respective details
And some of the first texts that they tried to print like this were buddhist text translated from Sanskrit (possibly via Tibetan).