The monastic tradition and Celtic spirituality for which Ireland is famous has formidable expression in many heritage sites across the island of Ireland, most of them in ruins. Inspiring though these may be, there are very few monuments to the country's history of faithful devotion to equal St. Patrick's Purgatory on an island in the Lough Derg that is tucked neatly into a peninsular corner of south-east Donegal surrounded by counties Fermanagh and Tyrone, and from which it takes its popular name. 

With Knock in Co. Mayo, where devotion dates from apparitions in the late 19th century, it has the distinction of featuring a century-old minor basilica as its principal building, adjacent to the site of an ancient cave reputed to have been used as a place of isolation and prayer by St. Davog, a disciple of St. Patrick (the cave was filled in and a church built over it in 1790); St. Patrick himself is not reputed to have any direct connection to the place).

The custody of this site has been in many hands since it first became a place of pilgrimage in the twelfth century, passing from the Augustinians to the Franciscans, and then in 1780 to the clergy of the diocese of Clogher. For many decades, the person appointed Prior of Lough Derg, a position combined with that of parish priest of Pettigo some three miles south of the island, did not have much of a profile other than in the immediate locality. This was despite the fact that since 1930 the island had a major church, given the title of basilica in 1931, and a large complex of buildings to accommodate the pilgrims who spend three sleep-deprived and fasting days there. 

The other national shrine and place of pilgrimage at Knock in Co. Mayo had a somewhat similar profile in the first part of the twentieth century. That changed when Father James Horan became parish priest there in 1967. Within a decade he had created a new focal point for the those visiting the shrine, which to that point had been the existing parish church on whose east wall had been mounted statues to indicate the positions of the figures (Virgin and saints) who had appeared there in 1879. The new structure was a large modern building, also given the title of minor basilica, designed by the Dublin architect Daithí Hanly, to accommodate 20,000. And within a further three years, Fr. Horan, by now Monsignor, had publicised his dream of building a regional airport into which the Pope could fly in 1979 to mark the centenary of the apparition (he missed that deadline by seven years, the airport being officially opened in 1986, some five months before Monsignor Horan died - coincidentally on pilgrimage to another Marian shrine at Lourdes in France, aged seventy-five).

The history of Lough Derg went back to a time more that six hundred years before the Knock apparitions. Around 1220, an early monastic community on the island in Lough Derg became an Augustinian priory under the Abbey of Saints Peter and Paul in Armagh, and the Celtic monastic rule gave way to a spirituality that was more pastoral in approach.  

In this phase, according to the official history of the place, ‘St Patrick’s Purgatory became renowned across Europe, drawing intrepid pilgrims from as far away as Spain, Italy and Hungary; literary references occur in Dante and Shakespeare and early printed maps of Europe always include St Patrick’s Purgatory.

Despite the destruction of everything on the island in 1632 by order of the local bishop, it was once again attracting 5,000 pilgrims a year by the turn of the century, a figure not greatly affected when in 1704 an Act of Parliament imposed a fine of 10 shillings or a public whipping as a penalty for going to such places of pilgrimage.

After the first chapel on the site was completed in 1790, the number of pilgrims increased so that by the 1820s as many as 15,000 pilgrims were coming to the Island and on the eve of the Great Famine the numbers had increased to 30,000 pilgrims.

The effects of the Famine reduced that number by ninety per cent, but the then Bishop of Clogher, James Donnelly, was insistent that facilities be provided even for these small numbers and so in 1882 a hospice for men was opened, to be followed some decades later by one for women (in the intervening period the diocese had been governed for fifteen years by Bishop Richard Owens, an uncle of Richard Mohan’s mother).

Throughout the first half of the 20th century the numbers grew to the point where by 1921 Bishop Patrick McKenna (like Bishop Owens a former staff member at St. Macartan's College and theology professor at Maynooth) embarked on an ambitious project - the building of a church dedicated to St Patrick in the Romanesque or Hiberno-Romanesque architectural idiom that was common in many Catholic churches built during the first decades of the twentieth century in Ireland, and particularly in the first decades after Independence. 

'The Romanesque Revival and Hiberno-Romanesque architectural styles harked back to the perceived ‘golden age’ of the Irish Church in the early Medieval period,' according to a Buildings of Ireland appraisal of the structure, 'and perhaps illustrate a reaction against the Gothic Revival styles of nineteenth century and British rule and a conscious desire to promote an Irish architectural identity in the new State. This central octagonal section is based on a plan derived from San Vitale in Ravenna, a building that the architect of the basilica, William Alphonsus Scott, had seen at first hand during travels to Italy in 1906' (Scott incidentally had an interesting connection with Maynooth, having designed the mausoleum in which the Irish scholar Fr. Eoghan O Gramhnaigh was buried in the college cemetery in 1906).

'The interior, which has a vaguely Byzantine character, is notable for the rich polychromatic marble detailing and particularly by the very fine series of fourteen stained glass windows depicting ‘The Stations of the Cross’ by the celebrated stained glass artist Harry Clarke', according to the Buildings of Ireland description.

'Thomas Joseph Cullen, a prolific and eminent architect in his own right, supervised the construction of Scott’s design after the latter's death at the age of fifty in 1921. Tenders were invited for building the foundations of the basilica in May 1924, and the total constructions costs were in excess of £80,000, an enormous sum at the time. The first mass was celebrated here on the 16th August 1929 and it was dedicated by the Bishop of Clogher on 12th May 1931.'

The availability of such an extensive facility created a new dynamic in the life of the area and the modest facilities for the handling of pilgrims from the pier at Ballymacvany, then a simple boat-launching station, now with its updated visitor centre and waiting area.

The long-term future of the location had been assured in 1960 when legal formalities were concluded whereby Sir Shane Leslie of Glaslough handed over all title to the lake and its islands to the Catholic Diocese of Clogher.

Visitor numbers fluctuated through the second half of the twentieth century although in the era of highest emigration during the 1950s more than 30,000 pilgrims visit the island over the traditional ten-week season from June 1.

But from the 1980s onwards, despite a decline in numbers, the future of Lough Derg as a place of pilgrimage was enhanced by the creation of a modern visitor environment that did not take away from the penitential aspect of the location.