Stonemasons embellished the arches and piers of Romanesque cathedrals with intricately carved patterns, and incised the outer wall of the aisle with interwoven arches. With these layers and details, the cathedral's builders and masons emphasized the colossal weight of stone that supports the _____________, while at the same time diffusing this effect of weightiness using surface ornamentation.
a) Clerestory
b) Tympanum
c) Buttresses
d) Vaults