Commonly given as birthday gifts or celebrations of a newborn, birthstone jewelry has much associated lore and legend. The first century Jewish historian Flavius Josephus proclaimed a connection between the twelve stones in the breastplate worn by Aaron in the book of Exodus (representing the twelve tribes of Israel), the twelve months of the year, and the twelve signs of the zodiac. The idea was that each of the gemstones had special powers associated with the corresponding astrological sign and wearing the stones at the right time would bestow the wearer with therapeutic or talismanic benefits. The idea of wearing the gemstone corresponding to one's birth month is a very modern idea that scholars trace to 18th century Poland. The modern list of birthstones was defined in 1912 by the National Association of Jewelers.