The historic marble coffin … with scenes of a Dionysian revelry with Dionysus and satyrs ... has been exposed to the elements for the last century and used as an oversized planter to grow tulips in in the rock garden of Blenheim Palace, Sir Winston Churchill's birthplace in Oxfordshire.
And for 100 years before that the 1,800 year old sarcophagus was used as a makeshift water feature by the fifth Duke of Marlborough who obtained it in the 19th Century.
Palace officials were prompted to take a closer look at the 6ft 6ins long object after an antiques expert spotted its ornate carvings while making an unrelated visit.
The palace had conservators remove the front marble section, which is the original part, and carry out an extensive investigation.
They identified the basin as a white marble sarcophagus depicting Dionysian revelry dating back to 300 AD.
Its splendid carvings depict a drunken Dionysus, the god of wine, leaning on an equally inebriated woodland satyr.
The pair are flanked by party revelers including Hercules and Ariadne as well as two large lion heads.
The marble section weighs nearly 500 kilos (900lbs).
The sarcophagus has been placed on public display in an underground room in Blenheim Palace.