The 2,200 year-old coin was found during excavations at Tel Kedesh in the upper Galilee. One side of the coin bears the name Arsinoe Philadephus II, the wife of Ptolemy II and the reverse side shows two overlapping cornucopia.
The authority said the coin was minted in Alexandria by Ptolemy V in 191 BCE.
Dr. Donald T. Ariel head of the authority's coin department told reporters the unusual size of the coin, which weighs almost an ounce, was apparently used for ceremonious purposes, possibly to honor Arsinoe II, the co-leader of Egypt with Ptolemy II, her husband and half-brother.
Ariel added it is the heaviest gold coin found in excavations in Israel, and one of the rarest finds to date.
"A coin this size wouldn't have been circulating in the markets, it would have had ceremonial purpose,"
He added that a coin of its size would have worth equal to a hundred silver coins, and the equivalent of half a year's salary for an above average person at the time.
Excavations at Tel Kedesh began in 1997, and the site where a large Persian/Hellenistic administrative building with reception halls, store rooms and an archive were found. The coin was found embedded in the wall of a room identified as the kitchen in the building, he said.
The excavations at the site are being carried out by the University of Minnesota and the University of Michigan.
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