Athens - Diggers accidentally discovered a temple to Zeus at the foot of Mount Olympus in an indicating that ancient Greeks switched away from polytheism to the faith of a single God even before Christianity appeared in Greece, archaeologists said on Friday.

The sanctuary was found during works to broaden the bed of the Vaphyras river running through the Dion temple complex at the foot of Mount Olympus, northern Greece - the seat of Greek mythology's twelve Gods.

The findings include the sanctuary's foundations, 14 marble blocks with marble eagles engraved on them - Zeus's symbol - and a slightly smaller-than-life-size, headless marble statue of Zeus, said archaeologist Dimitris Pantermalis who supervises the Dion site.

The sanctuary dates to the centuries preceding Christ's birth. Insignia found on it refer to Zeus as "the highest".

"It is a special version of Zeus as a single God residing in heaven... we know that 'Zeus the Highest' played an important role in the transition to monotheism," Pantermalis said.

"The findings are dated before the birth of Christ, that's what's important," he added.

It is the first time that a sanctuary to 'Zeus the Highest' is found, Pantermalis said.

Excavations continue and more findings are expected, possibly the marble statue's head, he added.

The Vaphyras river has often flooded the Dion site in the past. - Sapa-AFP