Built in the 11th century, the mica-slate and granite round tower stands about 30 meters (98 feet).
Its primary historical function was as a bell tower. However, it did not house a massive swinging church bell.
Rather than pulling a rope attached to a giant bronze bell, the monk at the top would ring a large, heavy hand-held iron or bronze bell. 
The inside of the tower was divided into six wooden storeys connected by steep timber ladders. A monk would climb all the way to the top floor.
The top storey has four windows facing different directions. The monk would lean toward or lean out of these windows to ring the bell, allowing the sound to carry across the entire valley.
Modern acoustic tests have shown that ringing a handbell from that height allows the sound to travel over two miles, easily calling monks back to prayer from the surrounding fields.