Officers raided a house in the eastern city of Bullas and seized 4,000 archaeological pieces, 5,000 rare coins, 100 paleontological and ethnographic artefacts, 40 paintings and 30 manuscripts dating from the 16th century.
One document found in the raid is a very rare manuscript written in Latin with gothic lettering and gilded capitals called the "Book of Psalms" dating from the late 14th or early 15th century, a police statement says.
Today's statement does not say exactly when the arrests were made.