william i, the first abbot of rievaulx, started construction in the 1130s. the second abbot, saint aelred of rievaulx, expanded the buildings and otherwise consolidated the existence of what with time became one of the great cistercian abbeys of yorkshire, second only to fountains abbey in fame. under aelred, the abbey is said to have grown to some 140 monks and 500 lay brothers. by the end of his tenure, rievaulx had five daughter-houses in england and scotland.