A priceless gold wreath has been unearthed in an ancient city in northern Greece, buried with human bones in a large copper vase that workers initially took for a land mine.

The University of Thessaloniki said in a statement Friday that the "astonishing" discovery was made during excavations this week in the ruins of ancient Aigai. The city was the first capital of ancient Macedonia where King Philip II - father of Alexander the Great - was assassinated.

The find is highly unusual as the rich artifacts appear to have been removed from a grave during ancient times and, for reasons that remain unclear, reburied in the city's marketplace near a shrine of the goddess Eukleia.

The "impressively large" copper vessel contained a cylindrical golden jar with a lid, with the gold wreath and the bones inside.

"The young workman who saw it was astounded and shouted 'land mine!'" the university statement said.

Excavator Chryssoula Saatsoglou-Paliadeli told The Associated Press the find probably dates to some time in the 4th century B.C., during which Philip and Alexander reigned.

"Archaeologists must explain why such a group ... was found outside the extensive royal cemetery," the university statement said. "(They must also) work out why the bones of the unknown - but not insignificant - person were hidden in the city's most public and sacred area."

During the 4th century B.C., burials outside organized cemeteries were very uncommon.