In the fourteenth century , the central piers ( upright supports ) of the crossing ( where the building forms a cross ) started sinking under the weight of the crossing tower . ` Scissor arches ' were inserted to brace and stabilize the piers as a unit . In the 14th century , the central piers of the crossing were found to be sinking under the weight of the crossing tower , so the `` scissor arches '' ( inverted strainer arches that are such a striking feature ) were inserted to brace and stabilize the piers as a unit .