In many countries around the world, the day considered unlucky is Friday the 13th. In Italy, however, it is Friday the 17th. The superstition derives partly from the Christian tradition (Friday is considered the day on which Christ died on the cross) but has its roots already in the era of ancient Rome, when the phobia of the number 17 (which also has a name, heptacaidecaphobia) spread in our peninsula.
Even if 17 was probably not well received by Pythagoras (with his devotion to numbers, it seems that he could not properly judge a prime number between two “perfect” numbers, i.e. 16 and 18), the association of the number 17 with bad luck definitively entered our collective imagination in Roman times. The reason is that, in Roman numerals, “17” was written XVII, whose anagram is vixi, that is, “I lived”, in the sense of: “I died”. “Vixi” was a funereal expression at the time and it didn’t take long for it to become associated with 17 and consequently the poor number was considered a harbinger of misfortune.
The superstition linked to 17 remained even in the Christian era. It was at that time that the nefarious power of the 17th was associated with Friday, considered by tradition as the day of Jesus’ crucifixion. For centuries, undertaking a journey, concluding a business deal or starting something new on Friday was considered a bad omen. The negative value of Friday ended up meeting with that of the 17th to give rise to the superstition, still alive today, that Friday the 17th is an unlucky date.
If in Italy the unlucky day par excellence is Friday the 17th, in most Anglo-Saxon countries (and, due to cultural influence, in a good part of the world) the feared day is Friday the 13th. The 13th was considered unlucky already in ancient times, probably due to association with the number of participants at the Last Supper (Jesus and the 12 apostles). The hypothesis has recently taken hold according to which the phobia of the number 13 would have been crystallized by the fact that the arrest of the Knights Templar took place on Friday the 13th (13 October 1307), but certainly the phobia of the number 13 (this too has a name, triscaidecaphobia) already existed before: traces of it can already be found in Norse mythology.
