St Brigid, having miraculously cured the King of Leinster of an unfortunate deformity, was offered all the land she could cover with her cloak in begrudging reward.

Unluckily for the mean-spirited monarch, Brigid called in some help from above and managed to drape her miraculous mantle over most of the open plain. It wasn't long before she had established a monastery and added religion to the region's traditional pursuits of racing horses and grazing sheep.

Happily for the profits of modern purveyors of fine hats and expensive frocks, little has changed since. The Curragh has remained the unploughed epicentre of Irish thoroughbred excellence and for one day each summer the fashion capital of Europe. The Irish Derby is the centrepiece of this weekend's flat racing festival, and although the line-up today looks to be light on quality, the race itself continues to build on a rich and colourful past.

It was first run in 1866 - almost a century after its English precursor at Epsom and just a year after an Act of Parliament had formally protected the Curragh for racing and sheep rearing for eternity.

Worried about the declining popularity of their favourite sport, a group of noblemen inaugurated the Irish Derby to provide a boost for the flat racing season.

Their project was a slow burner. A grand total of three horses showed up for the first renewal which was won by a horse called Selim. A couple of years later Madeira turned over the three to one on favourite Bee Sting in a race that only attracted two runners.

The race struggled along for several decades until Orby's victory exactly 100 years ago. This was a turning point for the race, a soap opera with a whiff of nationalism and revolution thrown in for good measure. Orby was owned by Richard 'Boss' Croker, who as a boy had escaped the West Cork famine and gone on to build a career in New York politics. He rose to prominence in the Tammany Hall machine that controlled the city at the time and used his political power to stockpile a corrupt personal fortune which he invested in luxuries such as art, expensive clothes, a massive estate in County Dublin - and a string of racehorses.

Croker had hoped to retire to England to pursue his interest in the turf but had been ostracised by the Newmarket elite and returned to Dublin to build a stable and plot revenge on his detractors. This finally arrived in 1907, when Orby became the first Irish trained winner of the Epsom Derby - and the first horse to be awarded the Freedom of Dublin. The patriotic pride in his achievement was evident when a woman reportedly congratulated Croker with the immortal line: "Thank God and you, sir that we have lived to see a Catholic horse win the Derby!" Ironically, The Boss was a Presbyterian.

Croker was keen to show off his horse to the Irish public and insisted on running him again three weeks later on unsuitably hard ground in the Irish Derby against his trainer's better judgement. Although he won at long odds on, the experience didn't do him any good and he broke down badly soon after. Orby was the first horse to win both the English and Irish Derbys and his ability, coupled with his owner's drive, helped to establish the Curragh race as an event of national significance.

None of the succeeding races enjoyed the same dramatic imprint of Orby's victory, although unusually for a classic race, there were two dead heats - one in 1924 and another 10 years later. Vincent O'Brien trained the first of his six winners in 1953 with Chamier and he followed this up four years later with Ballymoss who went on to win the St Leger, the Eclipse, the King George, the Coronation Cup and the Arc de Triomphe. His subsequent victories mark him out as the first undisputedly great colt to win the Irish Derby.

Three years later his trainer was embroiled in one of the races biggest controversies. In May 1960, O'Brien had his licence withdrawn when Chamour tested positive for an almost immeasurably small amount of a banned substance when he won a Curragh maiden. The horse subsequently won the Irish Derby, but with Vincent's brother, Phonsie, listed as the nominal trainer. O'Brien sued the Turf Club and won an apology for any suggestion of improper practice.

The problems the Irish Derby faced in fully integrating into the international classic season were finally solved in 1962 largely through the vision of the founder of the Irish Hospital Sweepstakes, Joe McGrath, who persuaded the authorities to allow the race to be sponsored. With the injection of Sweepstakes money, the race immediately became the most valuable Derby in the world and the prize fund increased from �7,000 in 1961 to over �50,000 in 1962.

The quality of the race rocketed. In the first 100 years of the race Orby was the only horse to win both the Irish and English derbies yet in 40 years of sponsorship there have been 14 dual winners as well as another four who have completed the French and Irish double. Since 1962 nine Irish Derby winners have been rated as one of the top two three-year-olds of that season, a list the previous 20 winners had been absent from. Statistically the race now matches the Epsom Derby as an incubator for future Group One winners.

The growth in prestige of our Derby has continued under the current sponsors, Budweiser, who will today conclude a 21year involvement in the race. During their time managing the purse swings, 12 winners of the race had already won or been placed in the French or English Derby's and the last six have collected three Arcs, two King Georges and two Breeders Cups between them. It has evolved into a seriously impressive race and even if today's looks relatively weak on paper, the winner is likely to go on to prove himself a lot better than the obvious entitlement of his current form.

It is now critical that the race attracts as generous a replacement as the current sponsor if it is to retain its position in an increasingly cluttered Group One calendar. Commercial Manager at the Curragh, Evan Arkwright, remains optimistic.

"We are working away on some serious options. It's just a question of putting the right kind of deal together."

Many of Ireland's foremost fashionistas will be among the 30,000 that trek across 'St Brigid's Pastures' this afternoon to watch 11 horses battle for Euro1.5m in prize money. If the light is right and the mist soft they may also catch a glimpse of some of the ghosts of derbies past, of Boss Croker or even the great Catholic horse, Orby, hacking up at 1-10. The authorities who have assiduously nurtured this old race over the years will be anxiously seeking a different kind of spirit. The ghost of future sponsorship.