The site was never empty. A ninth-century monastery had stood here, whose only surviving trace is a fragment of cross-shaft in the cemetery known as Bully's Acre, four hundred metres to the west. In 1174 the Anglo-Norman warlord Strongbow founded a priory on the same ground for the Knights Hospitaller - the warrior monks whose order, after their banishment from the Holy Land, had drifted across Europe taking in pilgrims and the wounded. The Kilmainham priory became their Irish headquarters. It survived Strongbow himself, generations of Norman lords, and the breakup of the Manor of Kilmainham, before Henry VIII closed it in the Dissolution of the Monasteries in the 1530s. The hill stood largely empty for a hundred and forty years, until the Duke of Ormonde decided to build something new on its old stones.

Sir William Robinson was Surveyor General to James Butler, the first Duke of Ormonde and Lord Lieutenant of Ireland. He had visited Les Invalides in Paris - Louis XIV's vast new home for war-wounded soldiers, completed in 1676 - and Ormonde had decided Ireland needed something similar for its own veterans. Robinson took Les Invalides as his model: a great quadrangle around a single enclosed courtyard, with a formal facade and a tall central clock tower. The first Master, Colonel John Jeffreys of Brecon, an old Welsh soldier who had fought for the Crown in the English Civil War, was appointed at three hundred pounds a year. By 1686 he was petitioning King James II for emergency funding - most of the original revenue streams had collapsed. The building survived; the soldiers moved in. Construction wrapped up in 1687. The following year Christopher Wren began the Royal Hospital Chelsea in London, taking his cue from both Les Invalides and Robinson's quadrangle on the Liffey.

The formal avenue leading to the Hospital ends at the Richmond Tower, a triumphal gate designed in the early 1800s by Francis Johnston - the great Regency architect responsible for the GPO and the conversion of the Irish Parliament into the Bank of Ireland. Johnston originally built the gate beside the Liffey at Bloody Bridge, now Rory O'More Bridge. When the railway arrived in 1844 and traffic clotted around the gate, it was dismantled and moved here piece by piece. During the dismantling the workmen made a discovery: above the arch, hidden behind a panel of wood painted to match the limestone, was Johnston's own coat of arms. He had set it there decades earlier in the expectation that the wooden cover would eventually rot away and reveal his signature to future generations - a private architectural joke. The arms were carefully removed during the move, and the gate now bears the official coat of arms of the Royal Hospital.

By the early twentieth century the population of pensioners had dwindled. When the Irish Free State emerged in 1922 there was brief discussion of using the Hospital as the home of the new Oireachtas, before Leinster House was chosen instead. The last old soldiers left in 1927 and the building entered a long limbo - used as a furniture store and even, at one point, as a depository for Lord Chancellor's state coaches. By the 1970s it was crumbling. In 1984 the Irish Government undertook a major restoration, and in 1991 the Royal Hospital reopened as the Irish Museum of Modern Art (IMMA). The seventeenth-century courtyards that had once echoed to the cough and shuffle of pensioned-off soldiers now hold rotating exhibitions of contemporary art - Sean Scully, Lucian Freud, Howard Hodgkin, Patrick Scott, the international and Irish collections curated together.

Every year on the Sunday nearest 11 July, the President of Ireland walks into the Hospital courtyard and lays a wreath. It is the National Day of Commemoration, marking the anniversary of the Truce that ended the Irish War of Independence in 1921, and it remembers all Irishmen and Irishwomen who have died in war - in the British armies of the First and Second World Wars, in the Irish War of Independence and Civil War, in the Defence Forces, and on United Nations service overseas. The Government attends. So do members of the Dáil and Seanad, the Council of State, the judiciary, the diplomatic corps, the Defence Forces. The choice of venue is deliberate. A building begun under Charles II for retired English-Irish soldiers, now housing modern Irish art and remembering Irish dead from every army of every century, anchors a complicated country's grief in a single courtyard. The rest of the year the grounds host concerts - Blur and Patti Smith and Tame Impala and the Forbidden Fruit festival each summer, ten thousand people on a lawn under the same roofline that Sir William Robinson drew in 1679.