To the modern mind a cameo ring is one that features a carved image of a woman. Typically they are worn exclusively by women. Neither of these characteristics are consistent throughout the history of cameo jewelry, though. They have been collected by at least one Pope and world conqueror. The history of cameo jewelry is both varied and extensive.
There are debates as to the true point of origin of cameos, but the main locations cited are the ancient civilizations of Rome, Greece and Egypt. Modern cameos are most often carved from sea shells, but the earliest versions were made from stone. Early civilizations paid tribute to leaders (both living and dead) on cameos. The Greeks and Romans used them to commemorate their deities. Various types of jewelry have always been made using cameos.
Pope Paul II was said to be an avid collector of cameos. During his life (in the 1400's) he was said to have amassed quite a collection of cameos of various types. This hobby started before he became Pope, but continued during his tenure. In fact, his love of cameos was blamed for his death. According to the reports at the time, wearing too many cameos on his fingers and hands caused his limbs to be too cold, which caused him to fall ill and die.
Cameos as Status Symbol
During the Elizabethan period (mid to late 1500's) women began to wear cameos as a symbol of prosperity. Since they were still being produced from stones, the cost of the jewelry was prohibitive to many common people. Therefore a large collection of cameo jewelry was thought to signify wealth. Thus the cameo was tied to the aristocracy and wealthy portion of society. Of course, that type of cultural significance adds to the appeal of an item.
The French Emperor and conqueror Napoléon Bonaparte was another male collector of cameos. He was said to have worn at least one cameo to his wedding. Perhaps his bigger contribution to the world of cameo jewelry came in his role of leader of France. He went so far as to establish a school devoted exclusively to the art form of cameo carving in Paris.
Cameos made from shells had been around for a while in some form for at least a couple hundred years, but didn't become popular until the 19th century. When the art of carving cameos was applied to shells (replacing stones as the predominant medium), the price of the jewelry was reduced. This allowed less affluent individuals to begin to buy rings and other jewelry featuring cameos and brought in the modern era of cameo popularity.