Catherine de Medici believed in astrology and magic (as did many in the 16th century - Elizabeth I had her own court astrologer, John Dee, who was also had as strong interest in cartography). In addition to patronizing Nostradamus, she also kept two Italians as her court astrologers - Tomaso and Cosimo de Ruggieri. Cosimo in particular had a dark reputation as master of the black arts. Tradition has it that he had kidnapped a baby, cut off its head, and kept the head alive so as to question it for dark secrets. According to Marshal de Metz, Catherine asked Ruggieri about the fate of her sons and the Valois dynasty. Ruggieri made for Catherine a magic looking glass (shades of Sleeping Beauty !) that Catherine could look into to foretell which of her sons would be king of France - the mirror showed each of her sons (except Herules) in the order in which they reigned, whose face circled the mirror a number of times corresponding to the number of years they reigned. After the face of Henri III (her last son to rule), there was supposedly a flash, followed by the Duke de Guise crossing the mirror; then there appeared the face of Henri of Navarre (the legal heir if the Valois line died out).
After the death of her husband the king, Catherine force her husband's mistress, Diane de Poiters, to trade a chateau on which Diane had spent a lot of money renovating for one of Catherine's - the Chateau of Chaumont. When Diane took possession of Chaumont, in one chamber she found the floor covered in chalk-drawn pentacles.