Hi Lynnda,

Thank you for contacting Mearto with your appraisal inquiry.
It's a little hard to tell exactly what this is because it is so worn but according to this website (http://www.ancient-roman-coin.com/antoninus%20pius-coins-imperial), it is a Gold Aureus, Antoninus Pius ( 140 to 143 ) - Rome. The loop on top was added later, so that this could be worn as a medallion, and while it's a genuine history of the piece, diminishes its value a little bit.
Based on the photos and information provided, and subject to examination, this is:

A Roman Gold Aureus, Antoninus Pius (140 to 143 CE) - Rome
Obverse: ANTONINVS AVG PIVS P P TR P COS III, laureate, draped and cuirassed bust right.
Reverse: SALVS AVG, Salus seated left, feeding serpent coiled around altar, from a patera, and holding sceptre.
about 1 inch round
CONDITION: worn and with later loop affixed to the top. not graded or case protected
PROVENANCE: acquired at auction
$400-600*
*represents a fair-market value for auction purposes; retail or asking price may vary.

Please let us know if you have additional items to appraise, and thank you again for using Mearto.