the abbey lies in a wooded dale by the river rye, sheltered by hills. the monks diverted part of the river several yards to the west in order to have enough flat land to build on. they altered the river's course twice more during the 12th century. the old course is visible in the abbey's grounds. this is an illustration of the technical ingenuity of the monks, who over time built up a profitable business mining lead and iron, rearing sheep and selling wool to buyers from all over europe. rievaulx abbey became one of the greatest and wealthiest in england, with 140 monks and many more lay brothers. it received grants of land totalling 6,000 acres (24 km²) and established daughter houses in england and scotland.