It’s Valentine’s Day, and as usual, people are presenting their loved ones with heart-shaped cards, candy, and trinkets. How did the heart shape become the symbol of true love?

Nobody’s quite sure, but it might have to do with a North African plant. During the seventh century B.C., the city-state of Cyrene had a lucrative trade in a rare, now-extinct plant: silphium. Although it was mostly used for seasoning, silphium was reputed to have an off-label use as a form of birth control. The silphium was so important to Cyrene’s economy that coins were minted that depicted the plant’s seedpod, which looks like the heart shape we know today. The theory goes that the heart shape first became associated with sex, and eventually, with love.

The Catholic Church contends that the modern heart shape did not come along until the 17^th century, when St. Margaret Mary Alocoque had a vision of it surrounded by thorns. This symbol became known as the Sacred Heart of Jesus and was associated with love and devotion; it began popping up often in stained-glass windows and other church iconography. But while the Sacred Heart may have popularized the shape, most scholars agree that it existed much earlier than the 1600s.

Less romantic ideas about the heart-shape’s origin exist as well. Some claim that the modern heart-shape simply came from botched attempts to draw an actual human heart, the organ which the ancients, including Aristotle, believed contained all human passions. One leading scholar of heart iconography claims that the philosopher’s physiologically inaccurate description of the human heart—as a three-chambered organ with a rounded top and pointy bottom—may have inspired medieval artists to create what we now know as the heart shape. The medieval tradition of courtly love may have reinforced the shape’s association with romance. Hearts can be found on playing cards, tapestries, and paintings.

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