According to a police announcement on Monday, the abbot and five more suspects attempted to sell the protected items – including two Gospels dated 1737 and 1761 – to an undercover officer for €200,000 ($215,000).
The arrests took place during a sting operation when the abbot allegedly tried to complete the sale. His assistant has also been arrested.
Four civilians have been taken into custody, as well. They are a pawnshop owner and his wife, a broker and another man accused of dealing in ancient coins, police said.
Authorities did not immediately release the names of those arrested.
The investigation is ongoing.
Founded in 362 AD in a cave in the Vouraikos Gorge near Kalavryta, the Mega Spilaio is one of the oldest monasteries in the Greek world.