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Ancient Greek ring -

This ring features a carnelian gemstone engraved with the Greek god Pan contemplating a theatrical mask. The piece dates back to the 1st century CE.

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Scarab ring -

The scarab ring is a style of finger ring featuring a small sculpture of a scarab beetle as the bezel (the thicker section of the hoop of a ring). They were a popular accessory in ancient Egypt and graced the fingers of several pharaohs, including Thutmose III. This example dates back to 1540–1069 BCE and features a turquoise faience mounted in gold.

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Key ring -

The original key ring was just that: a key mounted on the bezel used by the Romans as both a means of carrying a key to their family valuables chest, and to demonstrate their status within the family.

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Oldest gold rings in the world -

Among the astonishing hoard of gold artifacts discovered at the Varna Necropolis in Bulgaria, which comprises the oldest gold treasure in the world, were several rings. The items date back to between 4,600 and 4,200 BCE.

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Signet ring -

More than simply jewelry, signet rings were essential in the early Byzantine period for sealing personal documents and validating wills and testaments. By the 6th century CE, most rings had a personal monogram, such as the block-letter format on this silver example.

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The Thame Ring -

The Thame Ring is a 14th-century reliquary ring. A double-armed cross forms the central motif, and the ring cover can be removed to reveal a cavity that may once have contained a relic. It's engraved on the back with a scene from the Crucifixion, and is inscribed in Latin.

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The Rose Ring -

The Rose Ring was unearthed during the excavation of the Rose Playhouse on Bankside, London. The Rose Playhouse was a contemporary and rival of the Globe Theatre, and saw plays by both Shakespeare and Marlowe performed. The gold ring, believed to date back to 1753, is engraved with the French inscription 'PENCES POVR MOYE DV'. The letters 'DV' stand for the Latin words Deo Volente, and the inscription translates as 'Think of me God willing.'

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Jewish marriage ring -

A 16th-century gold Jewish marriage ring, the bezel formed as a high pitched enamel opening by a hinge strap and inscribed inside with a Hebrew inscription: mazel tov (congratulations).

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Mycenaean gold signet ring -

This fabulously detailed Mycenaean gold signet ring pictures a fertility rite. Lion-headed genii conduct libations in front of a goddess who holds a stemmed chalice. The ring dates back to 1,300 BCE.

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Memento mori ring -

A rather macabre piece of jewelry, momento mori rings were popular from the 16th through to the 18th centuries. Memento mori is a Latin phrase meaning "remember that you will die."

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Poison ring -

Also known as a pillbox ring, these rings were popular in Europe in the 16th century. A container under the bezel or inside the bezel itself could be used to hold poison or another noxious substance. The poison ring was used either to slip poison into an enemy's food or drink, or for the use of the wearer if they were taken prisoner. It's rumored that Lucrezia Borgia wore such a ring. 

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Friendship ring -

This 18-carat golden friendship ring shaped like a belt and buckle is said to have belonged to celebrated Irish playwright Oscar Wilde (1854–1900).

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Pre-engagement ring -

Marilyn Monroe's grape jelly garnet ring, a gift from her second husband Joe DiMaggio. The ring, which originally belonged to DiMaggio's mother, was given to Monroe as a pre-engagement ring (also known as a promise ring) by the American baseball legend.

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Marriage ring -

This rare, 6th-century CE octagonal marriage ring is decorated with eight scenes from the life of Christ, with the Ascension seen on the flat surface of the bezel (top). Protective powers were attributed to scenes of the life of Christ, and here they combine to form a prayer in pictures.

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Sewing ring -

Very early thimbles, like this hand dimpled soldered cylinder example, were fashioned almost as rings rather than the later hard pitted cup style.

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Thumb ring -

Thumb rings were designed to protect the thumb during archery. Some were of very elaborate design such as this example, made in India from agate in the 17th century.

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Ring of the Fisherman -

Also known as the Piscatory Ring, this is an official part of the regalia worn by the Pope. Pictured is the ring currently worn by Pope Francis, who eschewed tradition and chose a silver Fisherman's Ring rather than a gold one. As head of the Catholic Church and successor of Saint Peter, who was a fisherman by trade, the Pope wears the ring as a symbol derived from the tradition that the apostles were "fishers of men."

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Chequers Ring -

The Chequers Ring is one of the few surviving pieces of jewelry worn by Queen Elizabeth I of England. The rare mother-of-pearl ring, set with gold and rubies, includes a locket with two portraits: one depicting Elizabeth, and the other traditionally identified as Elizabeth's mother, Anne Boleyn.

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Doctoral ring -

In Danish, Norwegian, and Swedish academia, a doctoral ring may be bestowed upon the conferral of a doctorate. Pictured is a Swedish doctoral ring in white gold from Uppsala university's philosophical faculty.

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Engagement ring -

A diamond and sapphire engagement ring given in 1796 by Napoleon Bonaparte to Joséphine de Beauharnais.

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Insignia ring -

Insignia or signet rings were first used in ancient times by religious leaders and Pharaohs. Later they would include a family crest and could be used to add the symbol to a wax seal on a letter. The Freemasons organization still use signet rings today. Picture is a collection of their designs. 

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Royal ring -

A gold ring, with portraits of England's Queen Victoria and Prince Albert, from around 1840. The bezel is formed of miniature medals of Victoria and Albert. It was made by Rundell, Bridge and Rundell, who became the royal goldsmith in 1789.

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Art Deco ring -

Pictured are two rings. The top ring is an Art Deco platinum bezel fancy cut diamond ring by Tiffany & Co. made c. 1920. The other ring is a platinum baguette and round diamond stylized dome ring, also from New York, c. 1935. Art Deco placed greater emphasis on very elaborate and elegant designs, featuring less-expensive materials such as enamel, glass, horn, and ivory.

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Championship ring -

Championship rings are presented to members of winning teams in North American professional sports leagues, and college tournaments. The rings have long been part of North American sports culture and are typically made of yellow or white gold with diamonds and other precious stones.

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Claddagh ring -

The Claddagh ring is a traditional Irish ring which represents love, loyalty, and friendship. It originates from the the Irish fishing village of the same name in Galway, and was first produced in the 17th century.

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Diamond wedding ring -

The first documented use of a diamond ring to signify engagement was by the Archduke Maximilian of Austria in the imperial court of Vienna in 1477, upon his betrothal to Mary of Burgundy.

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Ruby ring -

For thousands of years, the ruby has been considered the stone of love, energy, passion, power, and represents a lust for life. It's one of the most popular gemstones for use in rings.

See also: MedicAlert: How a piece of jewelry may save your life

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