If you suffer from triskaidekaphobia, you’ll have a tough time today. The word means “fear of the number 13,” and today is Friday the 13th.

How did this seemingly innocent day get such a bad rap? It’s because of superstitions surrounding both the number 13 and Fridays in general. Here are some examples of events and circumstances which have given notoriety to Friday the 13th.

In ancient times, Friday was the day of the pagan goddess Freya, and 13 was her sacred number, because the pagan calendar had 13 months. Christian monks considered anything having to do with goddesses to be unlucky, and anything having to do with pagans as being evil. When pagans worshipped Freya on Friday the 13th, the monks accused them of “devil worship.”

For some, the number 13 is also considered to be unlucky because Jesus Christ was the 13th guest, in addition to his 12 Apostles, at the Last Supper, which took place the night before he was crucified — on a Friday.

The Bible points to Friday as being the day Eve gave Adam the apple.

Ancient Norsemen used 13 knots in the nooses they used to hang people.

In the 19th century, Lloyd’s of London refused to insure any ship sailing on Friday the 13th. The U.S. Navy still won’t launch ships on that date.

Hotels and office buildings often don’t have a 13th floor. Rumor has it there’s an organization in France that exists solely to provide last minute dinner guests, so there’ll never be 13 people at a table.

The ill-fated Apollo 13 mission was launched at 13:13 military time, and had to be aborted on April 13, 1970.