Smell is a powerful but mysterious force. This expert is on a quest to better understand it

What do you reckon a blend of dog poo, mouse guts and garlic would smell like?

Britta Ager knows exactly, after she carefully followed an ancient incense recipe to create the concoction.

"It was hands down the most disgusting thing I've ever smelled in my life. My entire house smelled like garlic and death," she says.

And that's just the point.

The Greco-Egyptian recipe demonstrates an ancient understanding of the power of smell — and how it can be used as artillery, says Dr Ager, a US classicist who specialises in scent in antiquity.

For example, in ancient Greece, if you wanted the moon goddess Selene to punish your enemies or bring you riches, you'd first try to woo her by saying prayers, offering a sacrifice or burning nice-smelling incense.

But if that failed?

Then you brought out the big guns.

A "coercive incense", like the poo-mouse blend, was designed to so enrage Selene with its foul smell that she'd appear "whether she wants to or not", Dr Ager says.

In everything from magic spells and potions, to religious ceremonies and everyday life, smell has been used "across the centuries … and across different cultures", she says.

For purposes both good and bad, people have tried to harness smell's potent force — one that is difficult to define and endlessly fascinating.

"It's so individual and it's so powerful."

Covering up blood and excrement

The ancient Romans and Greeks developed a "hierarchy of the senses" that we in the western world have largely inherited.

The hierarchy positions sight and hearing — the "intellectual senses" — as the "most important for navigating the world". The "animalistic senses" of smell, taste and touch are secondary, Dr Ager explains.

And so, seemingly relegated to the lower rungs, smell can be easily dismissed as irrelevant.

For example, you may have looked at ancient artworks in a museum or read early literature, but have you given much thought to the smell of an ancient city?

If the answer is no, you're missing out on a significant clue as to what life at that time was like.

"Roman cities must have smelled terrible," says Dr Ager, the author of The Scent of Ancient Magic.

At religious sanctuaries, for example, where sacrificial animals were slaughtered, there would have been smells of "a lot of blood and excrement", she says.

"But it's not how the ancients talked about these sites. They talk about them as smelling of incense and divinity."

That's because the early Romans were "really interested in curating their environments and making them smell nice", she says. 

Smell was being considered constantly thousands of years ago in ancient Rome, Greece and Egypt, in ancient Chinese and Mayan society, and beyond.

Then, as now, perfumes and incenses were used at parties and to mark special occasions.

Ancient Greco-Roman love spells relied on the smell of burning myrrh, while practising magicians burned incense, chewed aromatic seeds and wore cinnamon sticks around their necks to create an atmosphere ripe for magic rituals.

Smell also features prominently in classical myths, Dr Ager says.

She offers the example of the Jason and the Argonauts story, where Medea orchestrates the death of her brother by luring him into a trap with the scent of magic herbs. She also puts a dragon to sleep with her scented potions.

Smells to distinguish from the 'ordinary world'

A different kind of power associated with smell — that of holiness and saintliness — has preoccupied people for "most of recorded human history", says Italy-based journalist John Last.

A particular — and pleasant — smell "has been associated with holy people for a very long time", he tells ABC RN's Counterpoint.

In the continuing quest to better understand why this is, Last interviewed various historians and priests.

He learnt that many Christian saints were said to possess a "kind of heavenly smell of flowers or violets … roses [or] chrysanthemums". It was considered "proof of their holiness", he says.

Take the first Christian martyr, the second century's Saint Polycarp of Smyrna.

"It was said that when he was burned on the pyre in the arena he produced this sort of beautiful smell, the smell of incense," Last says.

Italian priest Saint Padre Pio has often been said to smell like violets, despite his "open, seeping [stigmata] wounds".

The myth of his smell helped construct "the idea of Padre Pio [as] the sort of unnaturally holy man, the man who transcended normal human condition and became closer to God", Last says.

He adds that another saint, Simeon Stylites of the fifth century, had rotten, worm-filled open wounds, but is nonetheless purported to have smelled "sweet".

"Throughout the ancient stories, you're getting this mingling of the smell of death and decay and rottenness with this sort of saintly nature."

He says scent has been used to "cover up stench" as well as "to create an aura of holiness" and a space "radically other from the ordinary world".

Indeed, the trade of incense was booming around the time of the Roman Empire.

"Incense was burned daily, by hundreds of different temples. It was a real sort of foundational part of daily life," Last says.

Transcending time and boundaries

Dr Ager believes part of what gives scent its potency is its immateriality.

She says there's a "wider human tendency to associate supernatural phenomena, magic, ghosts [or] gods … with scent".

"It's a kind of everyday model for how something invisible but powerful might work to us."

Interestingly, there are also "very few biological imperatives in our reactions to scent", she says.

"Humans all tend to have a strong negative reaction to rotting smells or smells of decay. And there seems to be a pretty universal positive reaction to sweet flowery smells.

"But in between there, our reactions are so personal and so individual, and often predicated on our personal histories.

"Scent is known for its flashbulb memory," she says.

"[It] triggers an immediate positive or negative reaction in us."

She wagers that most of us probably like the smell of baking bread or cinnamon. But we probably like a couple of weird smells, too.

"For example, I love the smell of turpentine and driveway sealer. These are not objectively nice smells, but they've got really good associations for me," Dr Ager says.

She explains that driveway sealer conjures up crisp spring mornings heading off to school while turpentine takes her back to art classes.

"Those are smells that I know a lot of other people hate, but [for me] they trigger really vivid memories," she says.

So while smell might seem to be lower in the hierarchy of senses, it is a peculiar and fascinating force.

"Smell is just kind of mysterious," Dr Ager says. "It transcends boundaries. It transcends time."