Why is 13 a bad number for a hotel floor?

In the dark ages, many smart women were branded as witches. In the bid to supress women, they were executed on Friday the 13th. hence Friday the 13th came to be considered as an unlucky day and 13 an unlucky number not only for hotels but for everything in general.some hotels don't have romm no. 13 at all.

The last supper Jesus + 12 disciples = 13

or simply

The Knights Templar were a monastic military order founded in Jerusalem in 1118 C.E., whose mission was to protect Christian pilgrims during the Crusades. Over the next two centuries, the Knights Templar became extraordinarily powerful and wealthy. Threatened by that power and eager to acquire their wealth, King Philip secretly ordered the mass arrest of all the Knights Templar in France on Friday, October 13, 1307 - Friday the 13th.