Dennis -- You have a special coin. You must have it checked out by a knowledgeable collector, a professional coin dealer, or, better yet, an authentication service such as PCGS, NGC, ICG, or ANACS (look them up on the Internet, do not use other services). Be sure you have a genuine coin, not an imitation of some sort. For top-notch, reliable coin dealers, see the PNG web site [Press Here].
'Normal' coins from Syracuse in Sicily with Arethusa, a mythological nymph, are valuable. We have a page on them at this link [Press Here]. But this coin is special. It has an impressive rendition of a Quadriga, or chariot drawn by four horses abreast, and a special portrait of Arethusa. We have seen these as large decadrachms and smaller tetradrachms.
DECADRACHM: about 42 grams
TETRADRACHM: about 18 grams
The drachm was a unit of weight equal to about 4.2 grams. Hence the decadrachm was ten drachms, and the tetradrachm four drachms in value.
Values are very high and scattered quite a bit. This is why it is important to get a thorough analysis of your specific coin. The example in our picture comes from Stack's Bowers and Ponterio where it is scheduled for auction with a starting price of $21000 US dollars. (As always, CoinQuest thanks Stack's Bowers and Ponterio for use of their coin photo.)
The best we can do is give a broad range of values for this coin, as follows:
DECADRACHM: $20000 to 150000 US dollars
TETRADRACHM: $500 to $5000
To reach these high values, the coin must have good eye appeal and be free of major problems such as large scratches, stains, spots, nicks, and gouges.
There are many bad replicas of these coins that would never fool a seasoned collector, but there are also better counterfeits that require serious inspection to be revealed as such. With coins with valuable, it is never a good idea to buy from a market stand on a street while on holiday in the Mediterranean - trust only professional dealers!
Good luck with your coin! If you can send an accurate weight and clear pictures, we may be able to give you a more accurate estimate of value. To do so, use the Contact link at the top of the home page to start an e-mail exchange.