Roman, 1st century BC / 1st century AD.
The ancient intaglio measures 1.4 x 1.2 cm.
The ring size is a O 1/2 UK / 7.2.5 US.
The high carat gold ring is modern.
The intaglio has historical damage to the bottom, however in the classical taste the setting edge of the ring incorporates a fine gold repair.
A similar intaglio can be found in the Museum of Fine Arts, Boston (accession number: 13.235) and another in the Michael C. Carlos Museum (object number: 2012.032.149).
An ancient marble sculpture known as the Borghese Centaur which dates to the 1st - 2nd Century AD can be found in the Musée du Louvre, Paris, catalogue number: MR 122 ; N 305 ; Ma 562.