Once they seemed indomitable, especially to the legions of girls who experienced the rigours of a convent school education.
But Roman Catholic nuns have become a dying breed and are facing an added threat - legislation which could threaten their charitable status.
With an ageing membership eroded by declining vocations - there are only 5,000 in England and Wales - clusters of nuns in their Sound of Music wimples are a rare sight.
Over the past few decades, religious sisters have gradually withdrawn from their historic roles of running schools and hospitals, to be replaced by lay counterparts or the state.
The decline began in the 1960s when, fired by the idealism of the times, many abandoned the confines of convent life in favour of the outside world.
Then, as the orders attempted to modernise in line with post-Vatican II thinking, they provoked another exodus - this time of more elderly nuns unnerved by the shedding of traditional values. Since then, the number of sisters in this country has halved, though there are indications that the decline is slowing.
Numbers have also dropped in Scotland - from 869 in 1994 to fewer than 700 - and even in Ireland vocations for the female religious orders have been drying up.
Some communities have survived by branching out into entrepreneurial activities.
The Congregation of Jesus, formerly the Institute of the Blessed Virgin Mary, which once ran independent schools in Ascot, Shaftesbury and Cambridge, have transformed their historic Bar Convent in York into a thriving bed and breakfast guest house, conference centre and tea shop.
Others earn an income by offering retreats for stressed executives.
But many orders have shrunk to a handful of members with an average age of 60 plus, leaving the few able bodied to care for the rest. They have been forced to sell their substantial religious houses and convents and move into often anonymous homes.
Although nuns live modestly, many communities are facing growing financial difficulties as fewer and fewer sisters are able to earn an income. One example is the small community of Dominicans in Cricklewood, north London, which is the home of Sister Raymunda Jordon, the general secretary of the Conference of Religious in England and Wales.
"There are seven of us, all over 60," she said. "One sister is 87, but she is still in good health and regularly visits the local care home.
"Another sister works in the care home. Another is in prison ministry, another teaches mathematics at a nearby comprehensive school. And we have two new vocations, one who is nearly 30 and another in her mid-40s. We live in an old vicarage big enough for eight people.
"These days we are making relationships with Muslims and other faiths in the area.
"It was at one time an all-Irish preserve but that's all changed - for the better perhaps."
She believes that society is tiring of unremitting materialism and people are once again seeking solace in shared spiritual commitment. "We are doing all sorts of work at a local level, something even the Government has recognised," she added.
But, in common with all religious bodies, the nuns could soon face the daunting prospect of having to prove that they are of continuing benefit to the public.
Under the draft Charities Bill, which is expected to be introduced into Parliament in November, the long-standing presumption that religious organisations are good for society has been removed. Sister Anne Thompson, of the Daughters of Jesus, warned last month that the test of "public benefit", which could affect the orders' charitable status, could prove a subjective one.
"Who can measure the comfort brought to a frightened old lady by a listening ear when a stone has been thrown through her window?" she asked.
"Who can measure the 'added value' to the economy by the additional years of contentment found through the patient daily mutual effort at respect, companionship and tolerance lived out in the community?
"How is the alleviation of loneliness, the comfort of panic or distress, the restoration of hope and the injection of humour into lives made dull and even intolerable by bereavement or isolation to be estimated?"
Sister Raymunda remains sanguine, however. "We should be accountable like everyone else, and we will always be active for the public benefit," she said. "People will always need our prayers and just someone to talk to."