Thirteen is the number most often named as unlucky in English-speaking countries, and the belief is so familiar that it is easy to assume it is ancient and well documented. The reality is more patchy. The best-known explanations are stories that were attached to the number, often long after the fact, and the superstition in its modern form seems to have become widespread mainly in the nineteenth and twentieth centuries. This article sets out the common stories, notes how reliable each one is, and explains the term for the fear. It describes beliefs, and does not suggest that thirteen has any effect on events.
Thirteen at the table
The most common explanation is the Last Supper. According to the Gospel accounts, Jesus shared a final meal with his twelve apostles, which makes thirteen people at the table, and one of them, Judas Iscariot, betrayed him. From this, a belief developed that having thirteen at a dinner invites misfortune, and in some versions that the first to leave or the last to sit will suffer. The Gospels themselves do not state any such rule about the number, so the superstition is a later interpretation of the scene. By the nineteenth century the belief was well established in parts of Europe, and hosts are reported to have invited an extra guest to avoid the number.
Twelve is an especially complete number in the biblical world, as the twelve tribes and the apostles show, so a thirteenth can look like an extra that breaks a complete set. That idea is plausible as one source of the unease, though it is an interpretation and not a documented cause.
The Norse story
A second familiar tale is set among the Norse gods. In the popular version, twelve gods were feasting in Valhalla when the trickster Loki arrived uninvited as a thirteenth guest, and the result was the death of the beloved god Baldr. The story is repeated in many books about the number, but it needs care. The surviving medieval Norse sources, mainly the Poetic Edda and the Prose Edda, tell of Loki’s role in Baldr’s death and of Loki disrupting a feast hosted by the sea-giant Aegir in the poem known as Lokasenna. They do not clearly tell a single story in which the thirteenth guest causes the death. The neat version appears to be a later combination of separate tales. As a result, it is best presented as a popular retelling, and not as evidence of an ancient Norse superstition about thirteen.
Other claimed origins
Several other origins are often mentioned, and most are weak.
- The Knights Templar were arrested in France on Friday 13 October 1307. The date is real. However, there is little evidence that the arrests created the superstition, and the link seems to have been popularised much later.
- The Code of Hammurabi is sometimes said to omit a thirteenth law. The claim is often repeated but is generally regarded as unreliable, since the numbering of the laws is a modern editorial convention, and it is not a sound basis for an ancient taboo.
- Thirteen lunar months do not fit neatly into a solar year, since a year holds a little over twelve lunations. This astronomical fact has been offered as a reason why thirteen disturbs a tidy calendar, but the connection with a taboo is speculative. Managing that mismatch is a recurring theme in the history of calendar systems.
Friday the 13th is more recent
The famous combination of Friday and the thirteenth is younger than either piece. Friday has had a reputation as an unlucky day in parts of the Christian world, in part because of the tradition that the crucifixion occurred on a Friday. Thirteen has its own reputation. The combination as a single dreaded date appears in the written record mostly from the nineteenth century onwards. One often-cited example is the death of the composer Gioachino Rossini on Friday 13 November 1868, and another is a 1907 novel by Thomas W. Lawson titled Friday, the Thirteenth, about a stockbroker who exploits the superstition. Reports of the date being feared before the nineteenth century are scarce.
In some other traditions, the unlucky day is different. In Greek and Spanish custom, it is Tuesday the 13th that carries the reputation, a reminder that “thirteen plus a bad day” is a flexible pattern and not a fixed rule.
What triskaidekaphobia means
The word triskaidekaphobia comes from Greek roots for “three”, “and”, “ten” and “fear”. It is generally credited to the American psychiatrist Isador Coriat in the early twentieth century, though the exact origin is not certain. The term is used for an irrational or excessive fear of the number, and for the milder habit of avoiding it. A fear of Friday the 13th has its own long name, paraskevidekatriaphobia.
In practice, most people who avoid thirteen are not afraid of it in a clinical sense. They are following a convention. The clearest example is the habit, in many Western buildings, of leaving out a thirteenth floor in elevator panels and room numbering, a practice that reflects the wider fear of thirteen. The building has the same number of storeys; only the label changes.
Not everywhere, and not always
Thirteen is not unlucky in every culture. In the Aztec ritual calendar, the tonalpohualli count combined twenty day signs with the numbers one to thirteen to produce a cycle of 260 days (20 × 13 = 260), and thirteen was simply part of the structure. Even within English-speaking cultures, the picture has contrary elements, such as the bakers dozen, in which a thirteenth item is a bonus for the customer.
Reading the superstition sensibly
The history of thirteen shows how a belief can feel old while being assembled from several parts: a religious scene, a mythic tale, a calendar oddity and a modern literary and media boost. Each part is attractive, and together they sound convincing. Careful sources point to a belief that grew gradually and unevenly, and that is stronger in some societies than in others. Whether the number appears at a dinner table or on a hotel door, it has no known power over events. What it has is a long record of stories.