Why is Friday 13th unlucky?

The ancient Romans believed that 13 was a bad omen, foretelling ill-fortune and death. The Vikings also hated 13, because in Norse mythology a banquet was held for 12 gods at which the trickster, Loki, appeared uninvited, like the wicked fairy in Sleeping Beauty, and as a result the beloved god, Balder, died.

The Mayans thought that the 13th 'baktun' (a period equivalent to almost 400 years) would spell the end of the world – however, this came and went in 2012.

For centuries, hosts avoided having 13 people seated around a dining table, convinced that the first person to leave would die within the year. Indeed, 16th-century witch-hunters often tried to claim there had been 13 people at a gathering – proof that the accused were witches in league with the devil.

The first written record we have of the number 13 and Friday being unlucky in conjunction only dates from the 19th century: "He [Italian composer Gioachino Rossini] was surrounded to the last by admiring friends; and if it be true that, like so many Italians, he regarded Fridays as an unlucky day and thirteen as an unlucky number, it is remarkable that on Friday 13th of November he passed away."

Despite its somewhat hazy history, the fear of Friday 13th is very real - it's even been given a scientific name (paraskevidekatriaphobia - from the Greek words Paraskeví, meaning Friday, and dekatreís, meaning 13).

Many people choose to stay in bed to reduce the likelihood of accidents, and it's estimated that in the US, as much as $900 million is lost in business each time as a result.

• Read next | 10 historical superstitions we carry on today

This content first appeared in BBC History Revealed