This is the true story of giant fennel birth control. Don't worry, fundamentalist religious leaders, it's extinct! Almost certainly. And maybe it wasn't birth control, maybe it was just a garnish. Or cough syrup. Or snake poison. Yeah.

Once upon a time (around 630 B.C.) there were way too many people on the Greek island of Thera. Then, according to Herodotus, a terrible drought killed all but one tree on the island. At the suggestion of the Oracle of Delphi, the Pythoness, they decided to send a bunch of citizens away to found a colony in North Africa. The Pythoness had to suggest this repeatedly, because nobody seemed to want to go.

Colonists were selected by lot, and when some tried to come back, the Therans threw rocks at them, so off they went, and eventually, with the guidance of friendly North Africans, settled at Cyrene (pronounced sigh-REEN-ee) in what is now Libya. Cyrene had a better climate than most of North Africa, and so the Therans farmed, and married Libyans, and made up a story about how their king was descended from Apollo and the nymph Cyrene. (Cyrene was guarding her father's sheep when along came a lion. She wrestled the lion to a standstill and Apollo, who was hanging around watching helpfully, the way gods do, was impressed and carried her off to Libya, where she had two children by him and one by Ares. Ares? Maybe it's better not to ask.)

Shortly after the colonists arrived, they discovered the amazing silphion plant, a form of giant fennel, which grew in a limited band along the Libyan coast. Linguistic evidence indicates that the Libyans already knew about silphion, but it was news to the colonists. Silphion was later called silphium or laserwort, and its juice was called laser, and everybody wanted some. Selling it around the Mediterranean made the Cyreneans rich. Or at least it made the rich Cyreneans richer, so they could spend their spare time racing four-horse chariots, something they picked up from the Libyans, and that means more jobs in the chariot industry for the less-rich.

They put pictures of silphium on their coins, sometimes with a female gesturing at it in a Vanna-like way. They were able to charge quite a bit for silphium, which was eventually worth its weight in silver. The Romans deposited it in their treasury.

There was one problem with silphium. They couldn't farm it. The Cyreneans grew everything from saffron crocuses to olive trees, but silphium wouldn't cooperate. Like the caper bush, Theophrastus noted, it would grow wild or not at all.

Silphium was a royal monopoly, with strict rules about how much could be harvested each year. The rules were broken, of course -- fennel-smugglers went through Carthage -- but not disastrously so. At least for the first five or six centuries.

But then silphium became extinct. Pliny the Elder (23-79 A.D.) wrote that in his lifetime only one stalk of genuine silphium had been found -- which was picked and sent to Nero. It's hard to pin down exactly when extinction happened, since when people couldn't get Cyrenean silphium they substituted "Syrian silphium," or asafoetida, a fennel of greater distribution. Asafoetida is known today chiefly for smelling just ghastly, unlike silphium, yet it was considered a reasonable substitute.

All this importing and rationing and depositing and smuggling and substituting sounds more like opium than fennel. What on earth was the stuff?

Based on ancient descriptions, and on depictions on coins, the consensus is that it was probably a species of giant fennel, which would have been put in the genus Ferula if it had still been around when Linnaeus was naming things. Some people think it may have been Ferula tingitana, which still grows in North Africa and the Midddle East. But it's hard to explain why the ancients wouldn't have noticed this valuable plant growing in places where they didn't have to pay the Cyreneans to get it.

What was so great about this particular giant fennel? This too, is somewhat unclear. Long articles have been written about silphium in which its use is glossed in a sentence or two: "highly esteemed ... in both the medical and culinary fields," one author notes airily. "Prosperity was based on grain, fruit, horses, and, above all, on an apparently extinct plant, Silphium," says the Encyclopedia Britannica, without a word about why silphium makes you prosperous.

It seems to have been a vegetable, a spice and a medicine. People ate the leaves, which resembled celery, and the stalks and roots. Aristophanes mentions grating it onto things as a garnish. Like parsley, say. Marcus Gavus Apicius suggested that when you fix boiled diced melon (pepones et melones), you should toss in a little fish sauce and a little silphium.

Medicinal uses mentioned by Hippocrates, back when you could still get real silphium, were as a purgative, for fever, for anal prolapse, for abdominal pain and for gynecological conditions.

Pliny the Elder repeats these, and also recommends it for sore throat, "warts in the seat," snakebite, scorpion stings, mange, gout, quinsy, epilepsy and more. He warns against stuffing silphium into your hollow tooth, because one man who did this then jumped off a cliff. He advises that, "mixed with wine it makes serpents burst, so very greedy are they for the wine," and so he thinks you might be better off not using it as toothpaste. Good for whatever ails you, apparently, unless you're a drunken snake.

Yet it doesn't really add up. Celery has never been worth its weight in silver and celery tycoons are hard to find. Parsley didn't get deposited in treasuries. Saffron is fairly rare and expensive, yet the Cyreneans didn't put it on their coins. Cough syrup doesn't get smuggled unless it makes you high. Not that many people suffer from warty seat or infestations of dipsomaniac snakes.

Recently some scholars, notably John Riddle, a medical historian at North Carolina State University, have suggested that the great value of silphium was as birth control. Hippocrates indicated that it can be used this way, either orally or perhaps the juice on a tuft of wool inserted as a pessary. It could be used either to prevent conception or as a (very early) abortifacient, uses that weren't distinguished. Some ancient authors say it was used "to control the menses," a phrase that, to this day, is often code for birth control. For decades, "controlling the menses" was the only approved use for birth-control pills in Japan, a fact to which Japanese women responded with an explosion of interest in pinpoint control.

As Riddle points out in his 1997 book "Eve's Herbs," there have been many plants used for contraception through the ages, from myrrh to Queen Anne's lace, yet little has been written on the subject. Rulers and governments don't usually approve of unregulated birth control, traditionally coming down on the side of More Taxpayers. They feel that if families are to be planned, they will do the planning.

Many classical authors disapproved of birth control, abortion or both, and downplayed such uses of medicines. Pliny, for example, merely said that Queen Anne's lace could be used to -- you guessed it -- control the menses, even though Hippocrates had already described its use as a contraceptive.

Riddle also points out that much information about birth-control methods was passed on by women, who were not writing medical texts. Any particularly female medical knowledge, therefore, could easily be lost in oral transmission, or, if not lost, remained invisible to scholars searching the written record. Tomes of Ancient Wisdom have relatively few entries under Girl Talk.

At one time, the most recent reference to Queen Anne's lace as a contraceptive that Riddle could locate was from the 17th century. Then he found himself in dinner-table conversation with a North Carolina public-health nurse, Mary Reichle, who mentioned that she had clients who used Queen Anne's lace to prevent pregnancy. Clearly the information had been passed on without making its mark in texts. (There's also a good reason some of this information isn't all over modern herbals -- most, if not all, effective abortifacients are extremely dangerous in overdose. But some people can't believe they could be harmful, because they're natural. Herbs! Dear, little fuzzy herbs! They would never harm me!)

There wouldn't be much use in passing on women's lore about silphium once it was extinct. Although Riddle is suspicious about the fact that some Appalachian hill people, until recently, wore a bag of asafoetida around their necks. What, for birth control? "Well, I think it was," Riddle told me. "People will tell you now that it was to ward off the devil."

(One herbalist says she believes asafoetida would make an excellent contraceptive, since it smells so rank it would keep possible sex partners far away.)

Since the histories are so vague about what made silphium sought-after, Riddle turns to literary references. There are passing references in some of the comedies of Aristophanes, but Riddle's favorite is a poem of Catullus, in which he answers Lesbia, his married lover, who asks how many kisses he'll be content with. Naturally Catullus makes the obligatory comparison to the number of stars in the sky (maybe the simile was fresher then). But he also compares the desired number with grains of sand in Libya, "where the silphium grows."

"In other words," Riddle crows, "'we can make love as long as we have silphium'!"

Classicist Nick Fisher, looking for possible references to this use of silphium, cites a lost Roman stage revue, "Laserpiciarus (The Laser-dealer)," featuring a popular song that Fisher translates as "Hey, Mr. Laserwort Man." You don't write a play like that about selling parsley.

Of course, this raises another herb-selling issue -- but no, if silphium were mind-altering, someone would've mentioned it.

The other category of high-priced, let's not-talk-about-it medication is the aphrodisiac. A drug with a reputation as an aphrodisiac can stay in business for centuries even if it doesn't work -- just ask Spanish fly. However, silphium isn't mentioned in that context.

If silphium was used for birth control, did it work? Lots of ineffective drugs stay in use, after all. But Riddle points to studies indicating that some other fennels, including asafoetida, the inferior "Syrian silphium," do indeed have contraceptive activity -- at least in rats.

It would be nice to test some actual silphium, but we don't have so much as a leaf of it left. Whether it was more like celery, parsley or the Pill, Cyrene had a good thing going with silphium, and fumbled it in a big way.

Like everything else about silphium, there's disagreement about what happened. The simple answer is that they picked it all. In a modern parallel, the recent popularity of herbs like echinacea and St. John's Wort (an antidepressant) is threatening some wild populations even when the plants are easy to cultivate. (St. John's Wort is so easy to grow that I, Gardener of Death, Susan of the Ten Black Thumbs, have a flourishing heap of the stuff. Admittedly, it is trying to sneak out of the planter box and make its way into somebody else's yard where it will be treated better, but it's healthy.) Silphium, a moodier plant than St. John's Wort, only grew in a small area. But they managed to harvest it for centuries -- what went wrong after that?

Pliny says that grazing animals, sheep in particular, ate it all. The Cyreneans could make more money off sheep than off silphium, he says. This doesn't make much sense -- the Cyreneans didn't put sheep on their coins. (And remember, Pliny is Mr. Exploding Drunken Snake Expert.)

Ancient Greek geographer Strabo and modern scholar Shimon Applebaum take the more complex view that the shepherds were increasingly disgruntled Libyans who weren't getting a cut of the silphium money, and so had no reason to keep the sheep out of the silphium patch.

Another theory, put forward by historian Alfred Andrews, is that things went wrong in 74 B.C., when Rome combined the Cyrene area and Crete into a senatorial province. Senatorial provinces were administered by governors who usually served for a year, and who got no salary. Their income was whatever they could wring from the province. They could get fast cash by leasing the grazing, and lost nothing if silphium sales went down in the future. "For a period of approximately six centuries, the supply remained unimpaired under careful control," wrote Andrews. "When this policy was abandoned, the plant became extinct in about half a century."

Whatever the details, this much seems clear: Silphium was not a "smart drug." It did not enhance the intellect. It did not have a clue printed on each and every one of its leaves, reading, "If you want to renew your prescription, don't burn down the drugstore." One moral of the story is that you can't rely on the magic of the marketplace to preserve a scarce resource. Like the physicians of the Middle Ages who specialized in ibex medicine and who then put themselves out of business by hunting the ibex to near-extinction or loggers into the modern day who harvest faster than they plant, the silphium tycoons -- eventually -- failed at long-term thinking.

Where does that leave the extinct giant fennel contraceptive? Quite possibly it was truly contraceptive. Quite probably it was a giant fennel. But is it really extinct?

The people who knew it, bought it, and used it were pretty sure it was extinct by the second century B.C. After that time, there's Pliny's account of the single stalk of silphium that was sent to Nero. And in the fourth century A.D., Synesius of Cyrene claimed there was some growing on his brother's farm. (Synesius was a Hypatian philosopher and then a Christian bishop. He wrote a piece that could easily be bouncing around e-mail humor lists, "In Praise of Baldness," about how the bald head is superior to the haired head in being more like a sphere, the most perfect thing of all. Scholars say he was kidding.)

In the 19th century, several expeditions to Libya went looking for silphium, but they either found nothing or found another species of giant fennel.

John Riddle says he went to a conference in Tunis a few years back, "just to get to that neck of the woods." He went for a walk, seeking silphium. "I saw some Ferula of a different species," he says. Would he recognize silphium if he saw it? "I'm not sure that I would!"

The other red herring is that, according to some scholars, if you go to the Cyrene area, the residents will point out a plant known to botanists as Thapsia garganica and tell you it's silphium, after you've just written pages and pages proving that silphium was not Thapsia, which grows all around the Mediterranean.

But could the diligent Cyreneans, even aided by their trusty sheep, really have wiped out every single viable seed? Couldn't silphium have made a secret comeback, unnoticed, in the wilder areas?

I recently heard a rumor, which I have been unable to confirm -- so far -- that a silphium plant has been found in Libya within the last few years. I am busily faxing in all directions in hopes of founding a worldwide all-natural birth control empire. I am ready to entertain offers of lavish funding for my expedition in return for my agreement to wear selected items of brand-emblazoned clothing. I simply need your promise that you won't dump me if it turns out to be parsley, and you won't feed it to my snake.