In Greek mythology, Hades, god of the Underworld, fell in love with the beautiful nymph Minthe. Hades’ wife, Persephone (the daughter of Zeus), became jealous and changed Minthe into the herb mint.
Hades could not bring Minthe back to human form, but he gave the herb a fragrant aroma and arranged it so that the more Minthe was trod upon, the sweeter her smell. Hence the popularity of mint as a strewing herb. In medieval times, strewn mint not only helped as an air freshener, but also had antiviral and antibacterial qualities that were reputed to combat the plague.
The pennyroyal (Mentha pulegium) species of mint has long been used as an effective flea deterrent. Pennyroyal, incidentally, is one species of mint that should never be taken internally. It is especially toxic to pregnant women and can cause miscarriages.