Disembodied Irish voices waft down from a solitary lilly-pilly tree in the courtyard of the Hyde Park Barracks in Sydney. The leaves rustle in a gathering wind, are subsumed by a raging fire. They went body and sleeves from the land. Taking the emigration. The words die out into the gentle lapping of water...

I am one of several Irish emigrants whose voices repeat the searing testimony of those who survived the Great Famine 150 years ago. Their legs swing and rock like the legs of a doll. They smell of mice. Boys? Or girls? You can't tell. Melbourne artist Paul Carter conceived this installation, fragments of unbearably moving words and song in English and Irish melded with environmental sound, 'to bear witness to an unspeakable disappearance... the fragmentation of human presences, the sweeping away of an entire way of life.'

Three bronze cast stools are casually arranged under the tree, as though their occupants had just left. A few metres away, a large section of the Barracks' sandstone wall has been dismantled and rotated on its axis, a symbolic rendering of the disruption and dislocation of the famine years. A bronze table intersects the stone wall as both a symbol of domesticity and sparseness and a link between the lives of those who stayed and those who left. Replacing the demolished wall are two glass panels inscribed with names, all female: Mary Rattigan, Bridget McMahon, Jane Dunford, Anastasia Brophy... The names fade towards the edges, lost to memory. A terrible stillness surrounds the sculpture, in spite of the city traffic. This work, by Iranian-born Hossein Valamanesh and his Welsh-Australian wife, Angela, is Australia's National Monument to the Great Irish Famine

The word 'famine' is as emotionally-charged for the Irish as the Holocaust is for the Jews. Between 1845 and 1849, from a population of over eight million, one million died and at least another million emigrated - proportionately more calamitous than even the huge famines of the Ukraine and China this century. The survivors were so traumatised it took 50 years for the Irish, normally so eloquent about loss, to even begin to talk about it. Oral histories collected in the 1890s struggle to describe the horror: as one eye-witness said, 'the living were out of their feeling.'

Although only about 20,000 Irish came to Australia as a direct result of the disaster, the famine created a culture of leaving which would eventually see 40% of Australians claim Irish descent. That leaving is only now starting to be reversed.

There is hardly a family in Ireland that has not lost someone in living memory to foreign parts. The figures speak for themselves: five million on the island of Ireland today, seventy million of Irish descent scattered around the world.

In Sydney, as the sesquicentenary of the famine approached, the Irish community wanted to commemorate the Australian legacy of those years. But how to adequately convey the shame, sorrow and anger the famine evokes, even still? How to find a human dimension in the horror? The answer lay with twenty shiploads of teenage girls.

On 6 October 1848, the Earl Grey entered Sydney Harbour. On board were 183 'orphan' girls, recruited from the workhouses of Ulster and offered free passage to Australia, there to become domestic servants. Over the next two years, 4,114 girls, aged between fourteen and twenty, would be sent from every county in Ireland to Sydney, Melbourne and Adelaide.

Although all were in the workhouse because they had no family support, some, like eighteen-year-old Eliza Fraser from Belfast, had one parent alive. 'Her father was a bootmaker. He was dead, but her mother was in New South Wales, residence unknown', says Eliza's great-granddaughter, Joan Dwyer, who has studied the family history. Dwyer believes Eliza's mother, Margaret, was given her ticket-of-leave around the same time Eliza arrived. 'To my knowledge, she never knew her daughter had come out to Australia as well. They never met. Margaret died alone.'

Even before the first ship docked, the 'orphan girls' were in trouble with the authorities. As historian Trevor McClaughlin documents in his book Barefoot and Pregnant, the surgeon singled out the 56 Belfast girls as 'notoriously bad... violent and disorderly, obscene and profane, many of them prostitutes'. Joan Dwyer is incensed at the assumptions made. 'I love the deposition from one of the constables in Belfast. He said, "just because people are foulmouthed doesn't mean they're unchaste." And I thought, thank you.'

The girls were disparaged for their job skills as much as their morals. Employers overlooked the fact that they were getting servants at bargain wages precisely because they were by definition 'apprentice'. According to the Melbourne Argus, they were 'the most stupid, the most ignorant, the most useless and the most unmanageable set of beings that ever cursed a country by their presence... whose knowledge of household duty barely reaches to distinguish the inside from the outside of a potato'.

Despite the dubious welcome, there was no shortage of volunteers from Ireland. When two girls died before one ship left, two others assumed their identities. Why? Because however hard and lonely life at the other end of the world might be, it could not have been worse than their native place, by 1848 reduced to what the transported rebel John Mitchel described as 'a dread, silent, vast, dissolution'.

The direct cause of the famine was a fungal disease that destroyed the potato crop on which much of the peasantry subsisted. But the reasons why a nation's existence could be so precarious are entwined with eight centuries of British colonisation, during which the Irish were systematically dispossessed of their land. What devastates schoolchildren to this day is to learn that grain was exported while people ate grass, starving tenants were evicted if they ate their cereal crops instead of selling them to pay the rent, and landlords hired firebrands to raze their homes. The authorities eventually provided some relief, but many of the homeless, destitute and dying had to do hard physical labour, building useless public works, before they were issued food. Roads that go nowhere still scar the landscape.

The word 'genocide' is often invoked when the Irish discuss the famine, but as one emigrant observed recently, 'they didn't even dignify us enough to try and wipe us out'. It was a passive annihilation, summed up in the langourous phrase of nineteenth-century economic rationalists, 'laissez-faire' - let it be. The land was 'overstocked' with tenants, so if an Act of God were to halve the population, so be it. The economy would be in much healthier shape as a result.

The idea of sending 4,000 orphans to Australia arose from similar economic pragmatism. It would relieve pressure on the already overflowing Irish workhouses, ease the labour shortage in Australia and help redress the gender imbalance. But as Charles Trevelyan, a British Treasury official noted, the Australians, 'although not quite so fond of a grievance as the excitable and imaginative Irish', might take it amiss if they thought they were getting substandard stock. He advocated sending two shiploads of Protestant girls first, to gild the pill. (A century later, immigration minister Arthur Calwell adopted a similar ruse, assuaging the latent racism of Australians by ensuring the first boatload of postwar European migrants were blue-eyed Balts, not swarthy southerners.)

But the girls on the Earl Grey and the ships that followed were mostly Catholic, and the predicted sectarian outcry ensued. It was led by the Presbyterian Minister John Dunmore Lang, who fulminated about Irish Catholic females 'silently subverting the Protestantism and extending the Romanism of the colony through the vile, Jesuitical, diabolical system of mixed marriages.'

Lang was right in one respect - the orphan girls, much more than other Irish emigrants, did tend towards mixed marriages, not just across religion, but across race. Trevor McClaughlin estimates that almost half married men of different religions, while the majority married Englishmen. Perhaps it was because, having no family networks, they had no-one to advise or criticise them. Or maybe they were innately more adventurous.

Joan Dwyer's great-grandmother, Eliza, wasted no time. Within four months she had married Edward Dwyer, an ex-convict transported for robbery. Lang would have been horrified: despite all the solid Protestant men in the colony, the Protestant Eliza chose a Catholic. Worse, although Lang had contended the Popish mothers would inflict their religion on the children, in this case Edward won out. But their first son, Joseph, restored things by marrying a Presbyterian. 'She was a good strong Orangewoman from Northern Ireland - and Catholic was never mentioned in the family again. She wiped it off the map.'

Most of the orphan girls married early. In Sydney, it was said that the Hiring Room at the Barracks resembled a meat market at times, but with eight or nine men to one woman in rural Australia, the girls could pick and choose. Many went for older men, perhaps because they offered security. Norah Shea married an Englishman seventeen years her senior and had eleven children. Her grandson was Sir Stanley Savige, the founder of Legacy, which supports war widows. Nineteen-year-old Hannah Raftery married an English Protestant but had a bet each way: they had both a Church of England and a Catholic ceremony. Johanna Kelly must have married for love: why else would an eighteen-year-old Irish Catholic go for a one-legged English Protestant twenty years older than her? They had forty-three years together.

Johanna Kelly lived to be 96 and produced twelve children. Some of the orphans were far less fortunate. The famine had taken a terrible toll on young girls entering adolescence. As historian Janet McCalman writes in Sex and Suffering, the Royal Womens' Hospital in Melbourne records that in 1860, 'one in fifteen of the patients born in Ireland had a contracted or deformed pelvis.'

When these young women became pregnant after years of proper nutrition in Australia, their babies developed normally - a dreadful calamity, as such big, healthy babies could not pass through their mothers' stunted pelvises. In a pre-Caesarian age, the only way of saving the mother's life was to kill the baby in utero and extract it in pieces. The Royal Women's Hospital records how in 1863, Irish-born Mrs M.C lost her third child that way. The following year, a Mrs M. O'C lost her sixth baby to the deformed, heart-shaped pelvis that was the legacy of the famine years.

Last September the Irish president, Mary MacAleese, visited the Hyde Park Barracks, where about 2,000 of the orphan girls spent their first days in Australia. Inaugurating the memorial sculpture, she pledged that the Irish government would contribute over one-sixth of the $300,000 cost. She praised the girls' courage, saying she could not imagine how her own teenage daughters could cope alone so far away even with today's telecommunications. Referring to the Earl Grey and the treatment of the Belfast girls, the president, herself from Belfast, commented acidly that she 'would have difficulty ever drinking that tea again.'

The orphan girls' presence was palpable. The Barracks displays the simple counter games they played to while away the time as they awaited their placement, a delicate orange rosary used for spiritual solace, endlessly-mended bonnets and petticoats showing the meticulous stitching that one historian lyrically describes as 'the handwriting of the illiterate'.

Some would also have crocheted. According to textiles curator Margot Riley, Irish women invented crochet during the famine to sell as fanciwork and save them from starvation. ( Do people consciously try to create beauty amidst horror or filth? I knew a night-soil collector down a mine who would do the most delicate, intricate crochet as he waited in the blackness for his mates' bowels to open.)

Menstrual rags are among their more curious legacies. The numerous rats in the building would drag away bits of fabric, including the girdles and strips of cloth used during menstruation, and incorporate them into their nests beneath the floor, where they remained undisturbed for over a hundred years.

Maria McDermott, aged fourteen, spent three months at the Barracks in 1849. Her older sister, Eliza, arrived the next year. At eighteen Maria got married in nearby St Mary's Cathedral, reputedly built with the pennies of the Irish poor. The marriage didn't last - 'that happened a bit in our family', says Maria's great-great-granddaughter, Terrie Pollard. Left to bring up her two children, Maria became a midwife and 'looked after the downtrodden', including prostitutes.

Pollard was already secretary of the famine commemoration committee when she discovered her own orphan girl links. Pride has replaced the anger she first felt for Maria and the family she lost in the famine. 'The strength of these women and what they did for the Australian personality - the fighting spirit, the contrariness, the sense of humour. How they survived was fantastic.'

On August 28, 150 years after Maria McDermott landed in Sydney, an ecumenical service will be held in St Mary's Cathedral where she got married. To the beat of the Irish bodhrán, 32 descendants of the orphan girls, one from each county in Ireland, will walk down the aisle to light a candle to their memory.

A stone's throw away, in the southern wall of the Hyde Park Barracks, is the sculpture in their honour. Former builders' labourer Jack Mundey, Chairman of the Historic Houses Trust and himself of Irish descent, used all his larrikin charm to persuade the more conservative members to make the site available. For two years, a committee chaired by Tom Power laboured to raise funds through everything from raffles to, ironically, gala dinners. The Land Titles Office, which owns part of the site, the Premier of New South Wales, the Lord Mayor of Sydney and the corporate sector contributed, as did individuals all over Australia, the USA, Ireland, Britain, and New Zealand.

The Valamanesh work, chosen from a field of forty-two, 'meditates... with dignity and irony on the legacy of absence', says Paul Carter. 'It will create a deep pool of silence in the midst of the noisy river of downtown Sydney... asking the visitor to slow down... to see in the visible and physical what is invisible, present but unspoken.'

Although Sydney's is called the National Monument, Melbourne has already paid tribute to the orphan girls. On 6 December last year, the 150th anniversary of the arrival of 191 girls on board the Lady Kennaway, a bluestone rock in Williamstown was dedicated to their memory, to serve as a stone both of mourning and of welcome. The simple ceremony was opened by Victor Briggs of the Bunurong people, in an acknowledgement that Irish and Aboriginal people had a shared history of oppression, and in regret that Irish had also been party to the dispossession of indigenous Australians.

Curiously, the unveiling of the Williamstown monument was criticised as 'romanticising' history, by none other than Janet McCalman, the respected historian who had written about pelvic deformities in Irish famine victims. With shades of the classic Monty Python skit about poverty ( "you were brought up in a cardboard box - luxury! Now me...), she argued that the Irish did not have a monopoly on suffering: Scottish Highlanders had also been dispossessed and yet were not painted as victims.

But the famine memorials are about celebrating life as well as lamenting the dead. 'If there's one word I describe these girls with, it's survivors', Joan Dwyer says, with feeling. 'Be honest about it - they were not maybe the most attractive people in the world. They might not be educated, they might be foul-mouthed, but there's no food and no work and they are strong, and prepared to do difficult things to survive.'

'I compare them with today's terminology on street-kids. They're not going to be nice middle-class people - they're just not going to be that - but that doesn't mean they're bad. With the right opportunities, they too can be the foundation of families for the future. That's what I like to hold onto the orphan girls for. Not because it's some romantic story of the past, but it's a story for us today to say what are we doing with our children? I know that Ireland feels sad at losing her girls. But I see it is as Ireland's gift to us. Four thousand-odd girls. It's a wonderful gift.'