This is a silver denarius of the Roman emperor Hadrian, who ruled from 117 until 138 AD. The galley on the reverse is a Praetoria Navis, the ship that would carry the commander-in-chief into a naval battle. In other words, it was a Roman flagship.
The sestertii (plural of sestertius) are made of bronze, and are much larger. They show the galley with more detail - on some types, there is even an inscription written on the sails. In the times these coins were minted, the emperor's name would often be embroidered unto the flags and sails of warships, supposedly in gold or silver.
Please see this CoinQuest page for more information, including an explanation of the 'COS III' inscription.
worn: $30 US dollars approximate catalog value
average circulated: $250
well preserved: $1000
average circulated: $850
well preserved: $2500
Both coins pictured on this page come from Roma Numismatics in London. The denarius in our main picture (upper left) sold for 400 British pounds (about $630 US dollars) in a 2012 auction. The sestertius in our secondary picture (to the right) did not sell, but was estimated at 2000 pounds ($3150 USD) by Roma. CoinQuest thanks Roma for use of their beautiful coin images.
Please refer to our Important Terminology page found at the top left in order to properly interpret these catalog values.