Phalluses adorned the ancient world. Over-sized erections were everywhere.

Instead of street signs, the Greeks placed monumental penises at road corners. Instead of door buzzers, Romans hung tintinnabulum – phallic figures decked with bells. Instead of decorating temple walls with instructive pictures, the Egyptians carved strutting, ithyphallic gods into the stone.

Erotic symbols, inscriptions and paintings so filled the streets of Pompeii and Herculaneum, that when the towns buried by the eruption of Vesuvius were first uncovered, hundreds of these items were squirrelled away to save embarrassed modern eyes. The British Museum had a room for obscene artifacts: the Secretum.

To penises you can add symbolic vulvas and wombs, in the form of wells and caves, passages and grottos – dark spaces to be dipped into or entered. And such representations are not only found in Europe. They’re widespread in India, in the lingam and the imagery of Shiva, and elsewhere. They’re primitive, earthy and universal.

And yet, it’s very hard for us today to sense why our forebears put gods like Priapus in the hallway; why they painted lovers in flagrante on their drinking cups; why they prized fine sculptures depicting gods copulating with goats. They didn’t even hide them from their children.

The seemingly pornographic tone of the ancient world struck me whilst holidaying in Ireland. We’d travelled to the Celtic isle to search out holy sites. What I’d not expected was the prevalence of thrusting columns and ritual crevasses in sacred places. They clearly conveyed the ancient fascination. The Hill of Tara is capped by a megalithic pecker. The so-called passage tombs of Newgrange and Knowth invite you in, if you dare. It’s not hard to see links between the pre-Christian imagery and the iconic symbol of Ireland’s medieval period: the nation’s numerous, magnificent high crosses that stand up in the sky.

It’s as if we’ve lost the imaginative equipment to relate to these shapes in ways that must, once, have come spontaneously, naturally. Instead, biology reduces them to pudenda, functional organs evolved for sexual reproduction. Or we see them in the light of the sexual revolution, evoking the promise of light-hearted pleasure. But there must have been more to erotics back then.

Take the Golden Ass by Lucius Apuleius. Written in the second century AD, it’s the story of Lucius’s metamorphosis into a donkey, through wizardry, and his return to human form by the power of Isis. Whilst an ass, he sees many things and undergoes numerous adventures, including a love-affair with a lady who seduces him. In fact, she is so impressed by the donkey’s amatory capabilities that she puts him on display. Lucius feels degraded and escapes.

The story was often told and illustrated in the ancient world, but are we to assume, simply, that Roman men found tales of women mounting male animals irresistibly exciting? The imagery was not for private titillation, sold in brown paper bags.

Maybe an imaginative, enriching link back can be found in another work by Apuleius, entitled On the God of Socrates.  It’s here that a famous proverb first appears, “familiarity breeds contempt”. And the treatise is, in a way, about how the familiar can be defamiliarized, and so reveal something unexpected, expansive and new. It’s what Socrates’ god did for him.

Lucius’ tale of becoming a donkey achieved that goal too. The vantage point of the ass releases him from being the ass that human beings so often are, or at least can be. It’s an initiation into a higher conception of experience and possibilities, hence the inclusion of the mystery rites of Isis. Lucius is born again.

Erotics must have spoken to the ancient mind in such a way. It was not just about the sexual – or at least, the familiar forms by being embraced or entered would convey a dynamic that was not only reproductive and pleasurable, but transformative. The stone phallus, for example, expresses a vitality that links to the sky. The standing stone looks like a giant pin between the heavens and the earth. They reach for the gods.

No doubt the deployment of them was also superstitious. The ringing of the tintinnabulum in the wind, or when touched, must have felt reassuring. The Hermes that stood on street corners must have offered protection against the evil eye that monitors your every turn. But that was only the beginning of it. Surely, the sacred womb was not just a place to hide but an origin from which to be reborn? Surely, the phallus conveyed a pronounced, active energy? Next time you see one, hug it and see! The thrust might keep devils at bay, but only because it invokes stronger forces for good.

But there is a twist that the erotic images present. Their good could only be known by the risk of being engulfed, consumed, penetrated, invaded. The modern writer who understands this element is Georges Bataille, the French author of the Erotism: Death and Sensuality. For Bataille, the erotic is that which upsets us. It is not natural: sex is natural, but the meaning human beings load onto the sexual lifts the biological into the imaginative and spiritual.

Bataille is like Freud who, contrary to the popular characterization, did not reduce everything to sex, but precisely the opposite. He realised that for human beings, there is no such thing as pure sex. Such acts are always already saturated with desire – the desire to conquer, submit, connect, experience, live, die.

To put it another way, the erotic is sacramental. These artifacts make hidden meanings manifest. Familiarity breeds contempt, remarks Apuleius, as happens when we moderns snigger at our forebears’ apparent obsessions. Do laugh, but do also sense the deeper energy they release.

For when we only see sex, and not symbol, we lose touch with an enchanted side of life. It’s a dimension found not only on mountaintops and in temples. It can be felt in the portals of doorways, or in the direction we chose when we make a turn on the street.